Chlorine in your plants? Yes. Well, sort of.
Before you go grab a jug of bleach, you need to know that laundry bleach most commonly refers to a dilute solution of sodium hypochlorite. This is NOT something you want anywhere near your plants. In fact, high concentrations of chlorine are fatal to all living things. It was even used in World War I as the first chemical warfare agent.
We are not quite ready to throw the book at chlorine, however. We need to know that chlorine is an element, much like copper or nitrogen, used by plants as food. You don’t hear much about it because plants only need it in tiny amounts. Once called trace elements, minerals used in such small amounts are now referred to as micronutrients. The form of chlorine used by plants is called chloride (Cl-).
Forms of chlorine
Chlorine is a highly reactive element. As such, it rarely occurs naturally by itself. Instead, it binds to other, nearby elements. In fact, chlorine will pair with practically every other element in the Periodic Table. Those parings occur because chlorine most commonly exists as an anion, or negatively charged, somewhat unstable atom, called chloride. To stabilize its outer electron field, chloride shares electrons with other elements, creating molecules. Some of these more familiar ‘binary chlorides’ include:
We all know ‘salting your fields’ ends badly for plants. Unfortunately, it can be difficult to know just how much chlorine is in your soil. Most soil tests do not include chlorine results. If your soil test indicates excessive levels of other anions, such as sulfur and boron, it may be difficult for your plants to absorb the chlorine they need. Only a lab-based soil test can tell you what those levels are and how they are changing over time. If you see signs of chlorine toxicity, you may want to limit the use of calcium chloride and potassium chloride.
How plants use chlorine
Chlorine aids plant metabolism during photosynthesis. It is necessary for osmosis and fluid balance within plants, working in tandem with potassium ions to open and close the stoma. As an anion, chlorine binds with many cations, or positively changed ions, helping to transport them throughout a plant. Chlorine also appears to have antifungal properties which are currently being explored.
Chlorine toxicities and deficiencies
Chlorine is a relatively mobile nutrient, which means it moves around freely within a plant, going wherever it is needed. This means that deficiencies are most often seen in older growth. Chlorine deficiencies appear as wilting, leaf mottling, and a highly branched but stubby root system. [Cabbages that are grown in chlorine deficient soils do not smell like cabbages.]
More often, chlorine toxicities occur close to swimming pools and in areas with hard water. [San Jose tap water ranges in pH from 7.0 to 8.7.] Symptoms of chlorine toxicity appear as scorched leaf margins, excessive leaf drop, reduced leaf size, and reduced overall growth. Too much chlorine can also interfere with nitrogen absorption, causing chlorosis, or yellowing, but that might not always be a bad thing.
We know that new growth tends to be more susceptible to disease than older growth. It ends up that chlorine’s interference with nitrogen uptake may be a method of reducing disease severity. As a disease occurs, plants absorb more chloride anions, blocking nitrogen uptake, and reducing the amount of vulnerable new growth being produced.
Now you know.
Gymnosperms are plants that produce naked seeds. We say they are naked because the seeds are not surrounded by an ovary. When seeds are enclosed by an ovary, which we generally refer to as fruit, the plant is classified as an angiosperm.
Angio- or gymno-?
There are several differences between angiosperm and gymnosperm:
Another difference between angiosperm and gymnosperm is the idea of softwood versus hardwood. Those terms don’t exclusively refer to the density of the wood. It actually points out that they are two entirely different types of plants. Hardwoods are angiosperms, while softwoods are gymnosperms.
Types of gymnosperm
Gymnosperm seeds, unlike angiosperm, develop on top of leaves or scales. Those scales often turn into cones. There are four existing types of gymnosperm:
You may have heard of pine nuts and gingko nuts, but neither one is actually a nut. True nuts are hard-shelled, inedible pods that hold both the fruit and the seed of a plant. The pod, or shell, of a nut is made from the ovary wall, which hardens over time. Hazelnuts, chestnuts, and acorns are true nuts. So are kola nuts.
A nut is not a nut when it is a fruit seed. Pine nuts and ginkgo nuts are not true nuts.
While most of the plants in your garden are probably angiosperms, you just might have a gymnosperm or two in the mix!
The red juicy bits found inside a pomegranate are called arils. Arils are a type of accessory fruit, or false fruit.
True fruits and false fruits
Fruit is the tissue that surrounds the seeds of angiosperms (flowering plants). Fruit is made from a plant’s ovary. Except when it isn’t. In some cases, a fruit develops from both the ovary and nearby tissue. These tissues can be either the perianth (flower whorls) or the hypanthium (the flower base). When this occurs, the part we eat is called an accessory fruit, or false fruit. Common accessory fruits include figs, mulberries, pineapples, and strawberries. Arils are specialized versions of these false fruits.
Arils are outgrowths that cover seeds partially or fully, which may or may not turn in to an edible fruit. This outgrowth originates where the seed attaches to the ovary, at the hilum. Along with pomegranates, the spice known as mace is an aril. Mace is a striking red aril that surrounds a nutmeg.
A slightly different version, called an arillode or false aril, emerges from a different location on the seed coat. Lychee, for example, grows partly from the hilum and partly from the integument or coating of the seed. The same is true for soapnuts. And yew creates a cup-shaped aril fruit, rather than a traditional cone.
Like other fruits, the aril serves as an attractant to herbivores. As birds, animals, and people eat these fruits, the seeds are spread farther and wides, improving the odds of continuing that particular line of genetic information.
Now you know.
Root hairs are where water absorption occurs. Since that water contains nutrients found in the soil, root hairs are important. And fragile.
You might expect root hairs to grow along the entire length of a root system, but that’s not what happens. Root hairs only occur in specific areas, or zones, of a root system.
Roots start out as undifferentiated cells. The very tip of a root is called the root cap, which protects the growing root as it moves through the soil. The next zone is where cell division takes place. As more cells are produced, the root cap is pushed forward. This growth is a relatively continuous process throughout the life of a plant. As new cells are produced and the root moves forward, the older cells stretch and create storage pockets called vacuoles. This is called the zone of elongation. Finally, growth and elongation are complete and root hairs can begin to emerge. This is called the zone of maturation.
The reason root hairs do not appear right away in the growth process is because they are so delicate that they would be sheared off as the root moves through the soil. This is also what causes transplant shock. The act of transplanting can shear off a majority of the root hairs as the soil gets jostled about and uninformed gardeners tamp down the soil. Rather than crushing delicate root hairs, mudding in new transplants protects those important root hairs.
Did you know that the reason root hairs are so evenly spaced along a root is because each hair secretes a poison that prevents nearby cells from producing their root hair? I didn’t either.
How root hairs absorb water and nutrients
Nutrient-rich water is pulled into the cytoplasm of root hair cells by osmosis. Root hairs also secrete malic acid, which helps convert minerals into ionic forms that are easier to absorb. Organic molecules in the soil, called chelates, also help root hairs absorb nutrients.
Root hairs as defense mechanism
Because root hairs are so small, they make it very difficult for harmful bacteria to enter the plant through the xylem. When beneficial bacteria, such as those which help legumes fix atmospheric nitrogen, appear, root hairs curl around the welcome visitor. This allows an infection thread to connect the two for everyone’s benefit. Helpful soil microorganisms, called mycorrhizae, are small enough to enter a plant’s root system through the root hairs. Root maggot larvae feed on root hairs.
Plants use phosphorus to grow healthy roots. Before you add more phosphorus to your soil, be sure to send out a sample for a soil test. Too much phosphorus can be just as bad, or worse, than not enough.
Nurse cropping is a form of companion planting in that specific plants are installed to provide one type of protection or another for young crops as they become established.
Nurse crops protect young perennials
In commercial agriculture, nurse crops are fast-growing annuals that are planted along with perennials, such as alfalfa, to help those perennials become established. This gives the long term crop protection from pests as it is getting started.
Nurse crops as trap crops
Trap crops are installed around or near desirable crops because of the way they attract or repel specific pests. In some cases, trap crops interfere with a pest’s lifecycle or kill it outright. In other cases, the trap crop is “harvested” after pests have appeared to remove them from the garden.
Nurse crops are frequently used as traps crops. For example, wireworms are a big problem for strawberries. In one study, strawberries planted alone had a 43% mortality rate, while strawberries planted two weeks before wheat was added had a 27% mortality rate. When wheat was planted 8 days before the strawberries, that mortality rate dropped to 5%. That’s a significant savings in strawberry starts, just by broadcasting a handful of wheat berries a week ahead of time!
Pros and cons of nurse cropping
Like every other plan of action, nurse cropping has pros and cons. The benefits of nurse cropping include reduced weeds, wind and erosion. Also, perennial seedlings are protected from excessive sun in their first weeks of growth. Oats and other cereals are common nurse crops. As such, another benefit is that the nurse crop can be a harvestable edible in its own right.
The potential problems associated with nurse cropping is that the nurse crop does use up water and nutrients. It may also become a type of weed itself.
You can use nurse cropping in your garden by starting cereal grains in a bed a week or so before planting something else. If you don’t harvest it, the local birds and other wildlife will appreciate the buffet and more tender plants will benefit, as well.
The way veins are arranged on a plant leaf can tell you a lot about that plant. That pattern of arrangement is called venation or veination.
There are complex classification systems for leaf venation, but all you really need to know is that there are four basic patterns: pinnate, palmate, parallel, or dichotomous.
Pinnate venation looks like a feather, with the primary vein emerging from the center of the base of the leaf and smaller veins, called veinlets, occurring at intervals and pointed outward at an angle. Pinnate venation is seen on citrus, walnut, and pistachio.
Palmate venation looks more like a hand with three or more veins radiating from the base. Grape, pumpkin, rhubarb, and sunflower are all examples of the palmate venation seen in most dicots and eudicots.
Two or more equal veins start and end together at the leaf ends while running parallel to each other through the middle. Parallel venation is common to monocots, such as millet and other grasses.
Dichotomous venation is seen as repeated forking or Y-branching, as seen in Ginkgo biloba leaves.
Other venation patterns
You may also run into a few other leaf vein arrangements that don’t conveniently fall into one of those four groups. For example:
When you are trying to identify an unknown plant, venation can help solve the mystery!
Ferns look lovely in a stumpery, but there is surprisingly more to ferns that you might expect
These plants have been around for over 350 million years, long before flowering plants, or angiosperms, made their appearance. Or dinosaurs, for that matter! Ferns are vascular plants that do not produce flowers or seeds. Instead, they reproduce using spores, similar to mushrooms and other fungi.
There are over 10,000 known fern species of fern [so far] and some species can live for 100 years. While some ferns are nearly microscopic, others can reach 80 feet in height.
There is a group of ferns (Azolla) found predominantly in water and they do not look like any ferns you might see on land. One in particular, the mosquito fern, is able to fix atmospheric nitrogen the same way land-dwelling legumes do before going to seed.
Ferns have three basic parts: rhizome, fronds, and sporangia. Fern rhizomes come in three forms: erect, lateral, and vertical. Erect rhizomes provide the solid base from which leafy fronds unfurl. Laterally growing, creeping rhizomes move above and below ground and may even climb trees. Vertical rhizomes often look more like the trunk of a tree.
Fronds are a fern’s leaves. The leaf stem, called a petiole when referring to other types of plants, is called a fern’s stipe. The flat blade of the frond is called a lamina. The lamina is often segmented into pinnae by short stems called rachides. When a frond first appears, it is tightly curled and called a fiddlehead or koru. Fronds perform photosynthesis and they provide support for a fern’s reproductive sporangia.
Black, brown, or orange sporangia are the reproductive structures of ferns. If there are no sporangia present, the fern is sterile. Normally found on the underside of the fronds, spores are formed in the sporangia. A cluster of sporangia is called a sorus. In some cases, a flap of tissue, called the indusium, may cover the sori until the spores are mature.
Ferns are unique in their method of reproduction and they are the only plants with two distinct living stages. As each spore matures, it becomes a sporophyte. Sporophytes that land in hospitable environments grow into very tiny, short-lived plants called gametophytes. Gametophytes have two sets of reproductive organs: a female archegonia and a male antheridia. Fertilization can take place within the same plant or between two neighboring plants. This fertilization produces a new sporophyte that grows into an adult fern.
While most ferns are not considered edible, they also tend to not be poisonous. There are some varieties of fern that are edible, such as:
As always, do not eat anything you are not sure to be safe.
Fern pests and diseases
Ferns are naturally resistant to most plant-eating insects. One edible fern in particular, Tectaria macrodonta, has a gene that was transferred to cotton plants, providing resistance against whiteflies! Foliar nematodes (Aphelenchoides fragariae) and soil borne nematodes (Pratylenchus) can sometimes be a problem.
Ferns are susceptible to diseases such as bacterial blight (Pseudomonas cichorii or P. gladioli), Pythium root rot, and Rhizoctonia blight. Infected plants should be discarded. Environmental problems, such as drought, which causes greying, and over-fertilization, which results in frond lobing and leaf tip burn, can be avoided with good cultural practices. This means investing in disease-free plants, using only as much fertilizer as recommended for each fern species, and avoiding overhead watering.
If you have a moist, shady crevice in your garden, ferns might be just what you've been looking for!
Heartwood is the dead center of a tree. It is usually a different color from the living wood and it provides the support needed to hold up a tree that might weigh several tons
Tree trunks are made up of several layers of tubes, surrounded by an outer layer of bark. These tubes are the vascular bundles that carry water and nutrients to the rest of the tree. One type of tube, called the xylem (or sapwood), pulls water and nutrients up from the roots. The majority of the trunk is made up of xylem cells. Another type of tube, called the phloem (or inner bark) carries the sugars made by the leaves through photosynthesis down into the rest of the tree. [I remember these two by saying, “Food flows down the phloem, while water and food rise in the xylem.”]
Just between the xylem and the phloem is the cambium layer. This is where the actual tree growth occurs. At the very center of the tree is the pith, surrounded by layers of xylem cells. As these xylem cells age, they eventually go through chemical changes that make them solid, losing their ability to transport water and nutrients. There is debate about whether or not these cells are still alive. This is the heartwood.
Characteristics of heartwood
Heartwood is very strong. The amount of heartwood present depends on the species. Some trees, such as ash, maple, and pine, have very thick heartwood. Other species have only a little heartwood. This group includes chestnut, mulberry and sassafras trees. Some tree species have no heartwood at all.
Heartwood gets larger over time. Young trees have very little heartwood, whereas older trees have significantly more.
Heartwood is resistant to decay, but wood that looks like heartwood might also be infected with disease or dealing with an insect invasion. Louisiana homes built over 100 years ago out of of bald cypress heartwood appear to be as good as new because of the decay resistance of heartwood.
The next time you need to remove a large branch or tree trunk, take a closer look at the layers and see if heartwood is present.
If you have ever canned jelly or fruit preserves, you have probably used pectin. Pectin is found in many plants and it has some unique properties.
The word pectin comes to us from the Greek word for “congealed” and with good reason. Pectin converts liquids into jelly, much the way gelatin does, the difference being that gelatin is made from animal skin and bones, and pectin is made from plants.
Pectin is found in most fruits, to one degree or another:
But fruits are not the only plants that contain pectin. Carrots hold an average 1.4% pectin. Commercially, most pectin is made from citrus peels and apple pulp. Soft fruits, such as grapes and strawberries also contain pectin, but at very low levels.
How do plants use pectin?
Pectin is a structural chain of molecules used in cell walls. Pectin is a major component of cellulose, specifically a layer called the middle lamella. The middle lamella is an outer layer to plant cells that is used to bind cells together. This allows plants to grow larger. The level of pectin present in a plant varies over time due to factors such as plant age and seasonal changes.
As fruits ripen, the pectin begins to break down, which is why the fruit becomes softer. A similar process occurs during abscission, when parts such as leaves naturally die and fall from the plant. In some desert plants, pectin has been shown to help repair DNA by creating a mucous layer that captures dew.
How do we use pectin?
Pectin is used for more than jelly making. Pectin also provides dietary fiber and it acts as a thickening agent and stabilizer for desserts, cosmetics, and medicines. Pectin also binds to cholesterol and slows the rate at which we absorb glucose. This is especially true when the pectin is from apples and oranges. You know that old saying about an apple a day? I guess they were right!
The pectin found in apple pulp is also one of the best throat lozenges I know. The mucilaginous pectin provides a surprising amount of soothing relief. Next time your have a sore or scratchy throat, skip the menthol (an irritant) and slowly eat an apple.
Molybdenum (Mo) is a plant micronutrient. So little is used that they used to be called trace minerals, but that doesn’t mean they are not important. Molybdenum is very important to your plants’ health.
Generally speaking, molybdenum is plentiful in alkaline soils and tends to be deficient in acidic soils. You can’t know what your soil contains without a soil test from a reputable lab. Those cute, colorful kits from the garden center don’t even test for molybdenum. Even if they did, they are not [yet] accurate enough to be useful.
How plants use molybdenum
Molybdenum is an essential ingredient to some very important enzymes. These enzymes are used in nitrogen, oxygen, and sulfur cycles. Specifically, molybdenum is used convert nitrate into nitrite and then into ammonia in order to be used to synthesize amino acids. It is also used by the bacteria responsible for converting atmospheric nitrogen into forms usable by plants. Molybdenum is also part of the process that converts inorganic phosphates into organic ones. Cruciferous plants, such as broccoli and cauliflower, and legumes, such as soybeans and clover, and citrus use a lot of molybdenum.
Plant nutrients are either mobile or immobile within a plant. Molybdenum is mobile, which means it moves around easily within a plant. This makes diagnosing deficiencies easier because they are most often seen in older leaves as plants pull nutrients to make new leaves. Molybdenum toxicity is practically unheard of, but deficiencies can be a serious problem.
Symptoms of molybdenum deficiency
Without molybdenum, leaves turn yellow and die and flowers may fail to form at all. The yellowing is often along leaf margins and downward cupping may also appear. In some cases, leaves develop a whiptail shape, rather than the leaf’s normal wider blade shape. Corn kernels may germinate on the cob prematurely in a last-ditch effort at reproduction. Legumes will have fewer or no root nodules if molybdenum is in short supply.
Again, you don’t know what your plants have access to without an inexpensive, lab-based soil test. Take my word for it, it is worth the effort.
Cabbage and mustard plants are probably not your first thought when it comes to fruit.
As strange as it may seem, the seeds and seed pods of radishes, broccoli, cauliflower, mustards, and other members of the cabbage family produce long, narrow, pod-shaped fruits called silique [se-LEEK]. If you only have one, it is called a siliqua [sil-eh-KWA].
More to pods than peas
Pods are a type of fruit that can be dehiscent or indehiscent. Dehiscent means that the structure opens spontaneously when its contents are mature. If a pod does not open automatically, it is called indehiscent. In either case, pods are made up of two identical long halves and they contain seeds. Those halves are called valves. Valves are the outer walls of the ovary. The two halves are joined along a seam, called a suture. Held between those two halves is a ribbon of seed-bearing tissue called the septum.
Siliquose fruit anatomy
If allowed to bolt, or go to seed, members of the cabbage family produce long, skinny fruits, commonly referred to as seed capsules or seed pods. These pods are each made from two fused carpels. The pods of legumes, such as peas and beans, are made from a single carpel.
If a seed capsule is more than three times as long as it is wide, it is called a silique, or siliqua. If a seed capsule is less than three times longer than wide, it is called silicle or silicula.
If you allow your radishes and other Brassicas to go to seed, you will see siliquae for yourself, plus you will have seeds for next year’s crop.
Now you know.
You’ve probably read dozens of articles and posts about the wonders of dish soap as a pesticide, fungicide, and surfactant in the garden. All of those posts are wrong.
How dish soap works
Dish soap, also known as dish washing liquid, is a detergent. Dish soap helps us get our dishes clean by cutting grease, oil, and wax. Dish soap generally contains colorants, fragrances, bleach, enzymes, phosphates, and rinsing agents.
Insects and plants have waxy coatings that are also damaged by dish soap. When this protective coating is removed, infection, pest infestation, and dehydration all become more likely.
Dish soap v. insecticidal soap
Insecticidal soap is not a detergent. It is a soap made specifically formulated for use on plants. And it must be used properly to be safe for plants and effective against pests. While liquid hand soap is a soap and not a detergent, it contains fatty acids which are phytotoxic, or poisonous, to plants.
Before trying a Quick Fix on your edible plants, take the time to research what is really going on. Your plants will thank you.
Over-fertilization is an increasingly common problem in home gardens.
It happens all the time. Your plants start out doing so well. Then they lose some of their vigor. You might see chlorosis (yellowing), cupping, less fruit production, or simply a failure to thrive. What is a gardener to do?
The traditional response was to add more fertilizer, manure, or aged compost. And it would work. For a while. Then those same symptoms would return, motivating you to add more fertilizer. And more. And more. Until it reaches the point where no matter how much fertilizer you add, your plants are simply not performing well. In fact, they seem more prone to pest infestations and diseases. How can this be?
Balanced plant nutrients
Just as we must eat a balanced diet to stay healthy, plants need access to a balance of nutrients. This is true partly because those nutrients are absorbed at the molecular level, as cations and anions, according to their electrical charge. Too many of one charge or the other makes it difficult for plants to absorb what they need. Also, some minerals, such as iron, are needed to absorb and use other nutrients. If there isn’t enough of these nutrients, or if they are made unavailable due to an imbalance, your plants can starve while sitting at a banquet. Mulder’s chart provides an image of what those nutrient relationships look like.
Too much of a good thing can be a bad thing. In the same way. too much of a nutrient can lead to toxic levels. Phosphorus, for example, is critical to plant growth and photosynthesis and it tends to bind tightly to soil particles. Phosphorus toxicity can lead to severe stunting and it blocks plants from absorbing iron and zinc.
Potassium is critical to enzyme reactions and water and mineral movement within a plant, helps prevent diseases, and regulates the rate of photosynthesis. Potassium toxicity causes leaf distortions, chlorosis, and yellowing along leaf margins. Potassium toxicity can cause calcium, nitrogen, and magnesium deficiencies.
Similar problems occur when there is too much of any nutrient. Compounding the problem, these excess nutrients often leach into rivers, streams, and groundwater, causing algae blooms that kill fish and create ripples of pollution and threats to biodiversity.
Too much of any one nutrient can throw a monkey wrench in the works. Too much of several nutrients can take years to resolve.
Is your soil over-fertilized?
The first step it to get a soil test. You don’t know what is in your soil without a soil test from a reputable lab. Sadly, those colorful over-the-counter soil tests are not accurate enough (yet) to be really useful. Many universities offer inexpensive soil tests. These tests can save you time and money and help your plants be healthier.
Below, you can see my soil tests from 2015 and 2019. In 2015, I learned that the property we bought had been over-fertilized for a very long time. Phosphorus and magnesium levels were critically high, and there was too much of pretty much everything. Except iron.
Remember what I said about iron and nutrient absorption? Yep, my plants had been sitting at a feast, unable to do more than nibble. And it showed. The plants in my landscape were prone to fungal disease, borers and other insects, and they simply were not thriving.
For four years, I thought I was doing better. I added a little iron. I avoided using any fertilizer, besides blood meal and ammonium sulfate (for nitrogen). But I continued to add aged compost to help reduce my compacted soil. My compost is mostly made up of chicken coop bedding. It ends up that chicken poop contains very high levels of nitrogen, potassium, phosphorus and calcium. While my plants needed the nitrogen, they certainly didn’t need any of the other nutrients.
How to correct over-fertilization
Looking at the results of my 2019 soil test, I realized that I hadn’t done nearly enough to correct my over-fertilization problem and had wasted 4 years in the process. Now, to correct the problem, I have stopped using my nutrient-rich compost on the ground. Instead, I am saving it for raised beds and container plants until my over-fertilization problem has been corrected.
And that’’s the cure - stop adding nutrients. The other half of the cure for over-fertilization is to remove nutrients by taking plant material out of your yard completely. Instead of grasscycling, bag and remove grass clippings. Or, you can add them to the compost pile or feed them to your chickens. Avoid using the chop and drop method for a while. Plant more heavy feeders, such as asparagus, beans, beets, broccoli, Brussels sprouts, cabbage, carrots, celery, corn, cucumbers, eggplant, garlic, leeks, melons, okra, onions, parsnips, peas, peppers, potatoes, pumpkins, shallots, squash, tomatoes, and turnips. And harvest those crops to within an inch of their lives. Take everything they have to give and get it out of your yard.
Armed with the results from my more recent soil test, I am now adding far more iron, to help my plants absorb what they need, and using wood chip mulch to counteract the compacted soil, but these actions will take time to have an effect. To monitor the effectiveness of these new actions, applying more iron and removing more plant material, I will switch to annual soil tests until the over-fertilization problem has been resolved.
I urge you to do the same.
Conifers produce seeds but not flowers. This makes them gymnosperms. Instead of flowers, conifers produce cones. Botanically known as strobili, cones are the reproductive organs of conifers.
There are male cones and female cones. Male cones, called microstrobilus or pollen cones, produce pollen and look very little like the cones we imagine. Male cones are more herbaceous than female cones and they look very similar to one another across species. Female cones are the familiar woody structures that produce and contain seeds. Female cones, also known as seed cones, ovulate cones, and megastrobili, are structurally unique to each species and helpful when it comes to identification.
Female cones are covered with plates called scales. Female cones start out as a central stem covered with bracts. Bracts are modified leaves or scales with a small flower or flower clusters in its axil. The bright red “petals” of poinsettia are not actually flowers. They are bracts. In some cases, the bracts harden and fuse to the woody seed scales.
Male cones appear in clusters and are much smaller than female cones. They contain pollen sacs and generally start growing on the end of the previous year’s branches, usually lower in the tree canopy, below female cones. This prevents self-pollination.
Cone and seed development
While male cones usually only last one year, it can take 3 or more years for a female cone to fully develop. Once a female cone is receptive and pollination has occurred, it can take up to a year for fertilization to be complete. As seeds develop, some cones will slowly begin to open, while other species need fire to trigger opening. Stone pine seeds, while delicious, require a lot of hard work to separate them from their cones.
Some conifer seeds have a wing that allows them to be carried on the wind, while other species rely on animals, such as squirrels, and birds help them disperse. Stone pine seeds, while delicious, require a lot of hard work to separate them from their cones.
Types of cones
The cones of holiday decoration fame are only one of many different types of cones. The scales can be arranged in one of two ways: imbricate or peltate. Imbricate scales overlap much like roof tiles and are attached along a common axis. Peltate scales do not overlap and are attached from a central point, more like an umbrella. Some cones look more like berries than cones.
Araucariaceae (monkey-puzzle tree, kauri, and the nearly extinct Wollemia tree) - fused scales create a spherical cone; imbricate
Cupressaceae (arborvitae, cypress, juniper, redwood, sequoia) - bracts and seed scales are fused; peltate
Pinaceae (cedar, fir, larch, pine, spruce) - archetypical cone; imbricate
Podocarpaceae (Prince Albert’s yew, Matai) - many of the scales are fused into a brightly colored, often edible aril; imbricate
Sciadopityaceae (Japanese umbrella pine) - imbricate
Taxaceae (yew) and Cephalotaxaceae (plum yews) - female cones have only one scale, with a single poisonous ovule; the surrounding fruit is sweet but the seed is deadly
While not conifers, cycads and welwitschia, or tree tumbo, also produce cones. Tree tumbo plants are considered living fossils and are unique in that female plants produce female cones and male plants produce male cones.
How many cone-producing plants do you have?
Plants are particularly thin-skinned. Did you know that a plant’s epidermis is only one cell thick? Just under that skimpy outer layer is a plant’s cortex.
The cortex is made up of thin-walled cells called parenchyma. Some of those cells are purposefully torn or separated to create air spaces. This porous tissue is called the aerenchyma [a-REN-ky-ma], from the Greek word for ‘infusion’. This word makes sense when you learn that the phloem is not the only part of a plant that transports nutrients. The cortex does, too!
The cortex is responsible for transporting nutrients and carbohydrates into the central core of a plant’s roots through diffusion. But there is even more to the cortex than just nutrient transportation.
Functions of the cortex
Depending on the plant, cortical cells may also store carbohydrates, essential oils, latex, resins, and tannins. in many cases, the cortex also contains chloroplasts that are able to perform photosynthesis, converting carbon dioxide and water into simple carbohydrates. Taking things one step further, the cortex can then convert those simple carbohydrates into the complex carbohydrates found in bulbs, tubers, and root vegetables, such as beets, carrots, and turnips. The cortex also manufactures the bark seen on the outside of woody plants and the underlying cork.
Cortex and water flow
In herbaceous plants, the innermost layer of the cortex is called the endodermis and the outermost layer is called the exodermis. The endodermis and exodermis are unique in that all of the cell walls have a woody band, called the casparian strip, except those facing the center or the outside of the plant. These casparian cells help regulate the flow of water between the vascular bundles, found just inside the cortex, and the outer cells of the cortex and epidermis.
Flax stem cross-section: 1. Pith 2. Protoxylem; 3. Xylem; 4. Phloem 5. Bast fiber 6. Cortex 7. Epidermis (Public Domain)
Pests and diseases of the cortex
Several bacterial diseases invade the root cortex through injury sites and natural openings. These diseases include bacterial wilt of beans (Curtobacterium), ring rot of potatoes (Clavibacter), cucurbit bacterial wilt (Erwinia), black rot of cucurbits (Xanthomonas), and Pierce’s disease of grapes (Xyella). The Pythium oomycete, which causes blackleg, also moves through the cortex. Dry, brown lesions seen in the main or taproot cortex can indicate Fusarium crown and root rot.
The next time you cut a plant stem or root, use a magnifying glass or hand lens to see what’s really going on in there. There are some amazing things going on in there!
Cavitation is the sound of water breaking.
While we don’t normally think of water being able to “break”, the columns of water that move upward through a tree’s veins can be broken, allowing air bubbles to form or simply severing a pathway for life-giving water.
Trees use a lot of water
The general rule of thumb for how much water a tree needs each week of summer is 10 gallons of water for every inch of trunk diameter, as measured at knee height. This means a large, mature tree, with a trunk diameter of 18”, will need 180 gallons of water every week at the peak of summer, on average. The flow of that water is critical to a tree’s health.
In healthy trees, water is absorbed through the roots and pulled upward through tubes called xylem. There are thousands of xylem in a mature tree. Picture the xylem as straws that run the vertical length of a tree. Water moves through xylem in a process called transpiration.
Transpiration refers to the way negative pressure is created within xylem as water evaporates from the surface of the leaves. This occurs because of surface tension, or the tendency of water molecules to stick together. When one water molecule leaves the plant through evaporation, lower water molecules are pulled upward.
Bubbles can be bad
Bubbles might be fun to play with, but bubbles in veins are bad. Just as air bubbles in an IV tube can kill you, so, too, can bubbles block the flow of life-giving water for a tree. Rapid transpiration can cause air bubbles to form in xylem. If too many air bubbles remain in place, it can kill a tree. Cavitation is much like an embolism for trees. Small, infrequent bubbles are not a serious problem. Large, fixed bubbles are deadly.
During periods of drought, the rate of evaporation on the surface of the leaves is so great that xylem can collapse and break, like a rope pulled too tautly. These breaks halt the flow of water completely, also killing a tree. Cavitation also occurs in response to thawing after water within a tree has frozen.
The sound of silence
If you could hear higher frequencies, it would sound similar to popcorn popping. In most cases, the frequency of this sound is too high for us to hear, but it can, occasionally, be heard. [It might be fun to try using a stethoscope on a tree…] I can only imagine that our peaceful summer walks in the woods sound more like a riot of trees screaming for water to our dogs…
Bottom line: make sure you irrigate your trees properly to keep them healthy, especially during summer.
Sometimes plants grow in ways you might not expect.
Instead of a nice round stem or flower, you get a flattened ribbon shape, or undulating folds, called ‘cockscomb’. This is called fasciation. It is also known as cresting.
Fasciation is a relatively rare physiological disorder that can create some really beautiful mutations. It can occur anywhere on a plant, but stems and flowers are the most commonly seen examples.
How does fasciation occur?
In normal plant development, growing tips (apical meristems) focus all their resources on a single point. This is what gives us straight and/or cylindrical stems and flowers. Fasciation elongates the apical meristem, creating a ribbon-like growth. The Latin word fascia means “a band” and can refer to anything that looks like a ribbon or wide band.
In some cases, these distortions can create unique bends, twists, and odd angles, or unusual clusters of growth that look like a witches broom. Flowers and leaves growing on these distorted stems may be smaller than normal, more abundant, or have other unique characteristics of their own.
One rare form of fasciation, called ring fasciation, has a ring-shaped growing point that creates hollow tubes.
What causes fasciation?
Fasciation can be caused by plant hormone imbalances, genetic mutations, environmental conditions, or bacterial, fungal, or viral infections. It can also occur for no apparent reason. Environmental factors include chemical overspray or exposure, mite or other insect infestation, and the presence of certain fungi. Exposure to cold and frost can also cause fasciation. Unless the fasciation is caused by bacteria, it is not contagious to nearby plants.
Plants affected by fasciation
In addition to my milkweed, this condition is most commonly seen on nasturtiums, geraniums, dandelions, and ferns. It has also been seen on fruits and vegetables, such as asparagus and broccoli.
Some plants are prized and propagated simply because of their fasciation. I look at it as a nice little surprise from the garden.
Have you seen fasciation in your garden?
Long, long ago, there were no flowers.
It wasn’t until the Cretaceous period, some 130 million years ago, that a handful of renegade cone-bearing gymnosperms started protecting their naked seeds with a new structure. This new, flimsy bit of color was so successful at boosting pollination rates that it spread far and wide, making flowering plants (angiosperms) one of the most successful types of plant life on Earth.
That structure is the petal.
Of course, that’s a pretty big claim for such a delicate flap of plant tissue. Too frequently discounted as an unimportant fashion accessory to more vital, functional parts of plant anatomy, there is far more to a flower petal than meets the eye!
Before we get to the really astounding stuff, let’s make sure we know what we are talking about when we talk about petals.
What are petals?
You may be surprised to learn that petals are modified leaves. In fact, sepals, stamens, and carpels are all genetic twists on the leaf. As a modified leaf, a petal has a broad, flat area called a blade. At the narrow end, where the petal attaches to the plant, is the claw, which is very similar to a petiole, or leaf stem. Where petals are attached to one another is called the limb. The petals that make up a flower are called its corolla.
Just under a collection of petals is another set of modified leaves, called sepals. Sepals are usually green. When discussing the combined petals and sepals of a flower, it is called the perianth. When sepals and petals are indistinguishable from one another, they are called tepals. [Aloes and tulips are tepals.] Sometimes, sepals look more like petals than leaves. When that occurs, they are said to be petaloid.
Petals of parentage
The number of petals present in a flower, the way the petals are arranged, whether or not they are fused to neighboring petals, or how much they are fused, as well as color are used by pollinators to find the pollen and nectar they seek. We can use the same information to identify unknown plants
First, flowers with 3 or 6 petals tend to be monocots, while flowers with 4 or 5 petals, or groups thereof, are most often eudicots, though not always. Petal arrangement, or floral symmetry, can also help with plant identification:
Petals, in particular, evolved to protect the reproductive part of a flower and to attract or repel specific pollinators. We know that flowers come in every color imaginable, but did you know that they also feature colors we cannot see, with glowing flight lines, traffic patterns, and welcome mats? It’s true! Flowers exist to attract the type of pollinator that will help them to procreate their species. Not all pollinators are created equally. It is a waste of resources for a plant (or any living thing) to attract the wrong sort.
The story of floral scent
Orchids produce floral scent in specialized sacs, but most flowers get their scent from chemicals produced by the petals. While many of us, along with most insect and bat pollinators, find floral aromas appealing, herbivores and disease-carrying insects often disagree with that evaluation. Combined with the colors, petal arrangement, and floral placement, floral scent works to increase a flower’s chance at becoming pollinated and/or fertilized.
Did you know that plants use floral scent to communicate with each other? It’s true! The volatile chemicals that give a flower its fragrance trigger a behavioral response in a surprising number of neighboring life forms and no two floral scents are identical, sort of like snowflakes.
Sensing a reproductively fertile neighbor, another flower may shift its chemical production to attract pollinators of its own. On the other hand, a fertilized flower will often release ethylene, a ripening agent, to discontinue the scent so that local pollinators will turn their attentions to neighboring flowers in need of pollinating. Also, injured flowers produce different scents than those being chewed on by herbivores. We can’t see it or smell it, but it’s going on all the time.
The Daily Garden is all about plant vocabulary. Today, we are looking at overall plant anatomy because it can be difficult to talk about something if you don’t know the words.
By taking a closer look at plant anatomy, we will be better able to understand each other, we can get more out of plant descriptions, and be better able to identify those mystery plants that always seem to pop up in the yard.
Plant anatomy, or phytotomy, starts with simple descriptions of the outside and inside of plants. Remember those black-line masters from grade school used to teach parts of a plant? Well, let’s start there.
Basic plant systems
Plants are have two basic systems: roots and shoots, with the root system below ground and the shoot system above ground. Roots provide anchorage and often store nutrients. Roots can develop as a taproot or fibrous root system. Roots have hairs that absorb water and nutrients. The shoot system consists of vegetative parts (leaves and stems) and reproductive parts (buds, fruits, seeds, and flowers or cones). Let’s take a closer look at each of those parts.
Leaves are the sugar factories of the plant world, absorbing sunlight and converting it into sugar through photosynthesis. The wide, flat part of a leaf is called the blade, or lamina. The shape of the leaf blade is very useful in plant identification, as is the way those leaves are arranged along a stem and the pattern of veins within a leaf. The edge of the leaf is called its margin. Leaves are coated with a waxy protective cuticle. There are tiny holes, usually found on the underside of a leaf, called stoma, that allow plants to exchange gases with the environment and to regulate water flow within the plant. The stem that connects a leaf to a stem is the petiole. Leaflike structures seen at the base of the petiole are called stipules,
Stems support leaves, flowers and buds. These structures are attached at nodes. The spaces between nodes are called internodes. Herbaceous stems have waxy cuticles for protection while woody plants have bark. Stems contain a vascular system that consists of the xylem, phloem and may include a cambium layer. This system carries food, water, and minerals throughout the plant. That vascular system is arranged in a circular pattern in dicots and eudicots, while it is more scattered in monocots. Twigs are woody stems from the previous year. Branches are more than one year old and may have lateral stems. Trunks are the main stem of woody plants, such as trees and shrubs. Canes are a type of stem filled with spongy pith. Canes generally only live for a year or two. Modified stems occur both above and below ground. Bulbs, corms, rhizomes, and tubers, such as potatoes, are below ground modified stems. Crowns, spurs, and stolons are aboveground modified stems. Thorns are also modified stems, but rose thorns are not really thorns. They are prickles, which are modified epidural, or skin cells. Stubby stems, called spurs, produce fruit buds.
Buds are shoots that may develop into leaves or flowers. Buds are identified by their location on a stem: lateral buds are found along the sides of a stem, while terminal buds are found at the end. Lateral buds usually grow where leaves meet the stem and are called axillary buds. Renegade adventitious buds may show up at injury sites, on roots, or even at the edge of a leaf. The place where buds fall off leave a mark called a bud scar. Tree leaf buds have scales, while leaf buds of annuals and herbaceous perennials have delicate naked buds. Potato eyes are clusters of buds.
Fruits are ripened plant ovaries. Fruits can be simple (formed with one ovary), as in the case of stone fruits, or compound (formed with several fused ovaries). Compound fruits can be multiple or aggregate. Apples and other pomes are multiple compound fruits. You can tell by the 5-pointed star shape in the center of the fruit. Raspberries, which are drupes, not berries, along with pineapples and figs are formed by many flowers fusing together and are called aggregate fruits. By the way, strawberries are not berries, either. They are ripened receptacles. Berries, such as pumpkins, cantaloupes, cucumbers, eggplants, and tomatoes, all have many seeds inside an outer shell of varying thicknesses and hardnesses. Dry fruits, such as peas and beans, grow in pods that either open down a seam (dehiscent), or stay closed (indehiscent), as in the case of peanuts and most cereal grains, such as wheat and barley.
Seeds have three parts: the embryonic plant, stored food, called endosperm, and a protective seed coat. As temperatures rise and moisture is absorbed through the sed coat, a primary root, called the radicle, will emerge, followed by the first stem, or hypocotyl. First leaves, or cotyledons often look very different from adult leaves.
Flowers exist solely to attract pollinators. Only angiosperms make flowers. Gymnosperms, such as conifers, ginkgo trees, and cycads make cones, or strobili. The colors, patterns, showy displays, and sweet aromas we associate with flowers are all in place to attract insects, bats, and birds. Flowers are supported by a stem called a peduncle. Small green leaf-like structure, called sepals, are often seen at the base of a flower. A collection of sepals is called a calyx. Individual petals may produce nectar or scent. All of the petals together are called the corolla. The combined corolla and calyx are called the perianth. The tip of a flower stalk, called the receptacle, contains the plant’s reproductive organs. Flowers can be male, female, or both, though not always at the same time. The female part, or pistil, consists of a pollen-receiving stigma, supportive style, and the ovary. [When you eat saffron, you are eating the style and stigma of an autumn crocus flower.] The male part, or stamen, consists of a pollen-producing anther and a supporting filament. Flowers are very useful in plant identification.
Genetic research and electron microscopes have brought plant anatomy to exciting new levels. Assumptions about kinship have been wrecked asunder and colorized scanning electron microscope (SEM) images can be breathtaking. Different types of plant cells gather together to create tissues. Those tissues come together to create the functional parts of a plant.
Ultimately, all those functional parts grow into delicious, nutritious foods that we can cultivate in our yards for decades. For me, feet up in the yard with a nice glass of wine beats standing in line at a grocery store any day!
What do wedges of citrus, hard walnut shells, the white bits inside a pomegranate, and the paper coating around avocado pits have in common?
They are all endocarps.
How can this be? How can structures so very different be the same part? Let’s find out by starting with some basic fruit facts.
The fruits and seeds we eat are plant ovaries. When a flower is pollinated and fertilized, three new structures form: seeds, pericarp, and placentae. Embryonic seeds attach to the placenta, and pericarp begins to grow, to feed and protect the embryonic seed, and to attract seed-spreading herbivores. There are three different types of pericarp tissue: exocarp (outer skin), mesocarp (flesh), and endocarp (inner layer). So, endocarp is the interior fruit that surrounds seeds. But what about all those differences?
Types of endocarp
Endocarp is generally not fruit in the way you would expect, unless you are talking about peppers or citrus. The fleshy parts of sweet peppers and chili peppers is the endocarp, as are those membranous wedges of fruity goodness found inside lemons, limes, and oranges. If you look inside an apple, the endocarp is the hard clear plate-shaped bits close to the seeds.
If you take a close look at a stone fruit, such as a nectarine or cherry, the endocarp is very hard and inedible. To us, it looks more like the shell of a nut. And guess what? The hard outer shell of walnuts, pecans, and almonds, that shell is the endocarp, even though, to us, it looks as though it is on the outside.
Confused? Read on!
Nuts about endocarp
When a nut develops on a tree, the exterior rarely looks like what you see in the grocery store. Many nut species have smooth or furry green exteriors (exocarp). That exocarp coats a hard, familiar shell. That shell is the endocarp of a nut.
You can grow a surprising amount of food in your own yard. Ask me how!