Phototropism

I've had this baby's tears plant (Soleirolia soleirolii) for just over 6 months now. This is the longest time that I've kept a plant alive! This plant is very adaptable (meaning it can survive under many different conditions) and is considered a weed in some areas, so there really would be no hope for me if I couldn't even keep this plant alive...

The stems grew and crept over the original pot, so much that the stems spilt all the way down the sides, so I recently re-potted the entire plant and gave it a haircut :)

Warning: (A Lot of) Science Ahead


You may notice that the leaves of the plant are facing towards the sun, as is the case with many plants. Scientifically, this phenomenon is called "positive phototropism" (positive meaning it grows toward the light; if it grows away from the light, it is called negative phototropism). I don't study botany, but from what I've read, it's a complicated process that involves the plant making different proteins (i.e. changing gene expression), and a very important class of hormones called auxins, which regulate plant growth and development. The central driver of phototropism is the uneven distribution of auxin within the plant stems. Auxin concentration is higher on the side of the stem that receives the least light, which causes the cells on this side of the stem to grow faster/more than the cells on the other sides, and the plant to grow toward the light.

In addition to light, there are many other stimuli that induce organisms, both plants and animals, to exhibit characteristic behaviours. Stimuli include, but are certainly not limited to, chemicals, temperature, and gravity. In immobile organisms, the response is usually growth toward/away from the stimulus, referred to as tropism. In mobile organisms, the response is usually movement toward/away from the stimulus, referred to as taxis. In both groups of organisms, if the response is non-directional, it is referred to as kinesis. :)

(I hope someone actually reads the science bit today. I spent so much time on it, researching and making sure the language is understandable, even for people who don't study biology... >.<)