All plants grow toward sunlight, except when then don’t.
In nearly all cases, plant stems, vines, and bines grow upward, reaching for the sun’s energy. Plants deprived of sunlight will often grow longer than they can support, in an effort to reach that energy source. This is called etiolation. But, sometimes, it is better for a plant to grow away from sunlight. This behavior is called skototropism.
The dark side
Light levels are pretty dim at ground level in a thick jungle. If a vine does not find a tree to climb, it will die. If it heads toward visible light (an opening in the canopy), it will never find a tree to climb. Instead, these vines must grow toward the darkest place they can find (the base of a large tree) in order to find something big enough, strong enough, and tall enough, to provide support. What’s really interesting, is that larger trees attract more vines, while smaller trees attract less vines. There are even mathematical formulas that describe skototropism among certain jungle seedlings!
Once a climbing plant has found a support structure, the skototropism behavior is turned off and upward growth (phototropism) begins in earnest.
[Some scientists believe that roots grow down because of skototropism, while others believe it is something called gravitropism. You decide.]
You can grow a surprising amount of food in your own yard. Ask me how!