section_path: In plants
section_name: In plants
paragraph_text: In plants
  
  Plants lack a specialized organ devoted to memory retention, so plant memory has been a controversial topic in recent years. New advances in the field have identified the presence of neurotransmitters in plants, adding to the hypothesis that plants are capable of remembering. Action potentials, a physiological response characteristic of neurons, have been shown to have an influence on plants as well, including in wound responses and photosynthesis. In addition to these homologous features of memory systems in both plants and animals, plants have also been observed to encode, store and retrieve basic short-term memories.
  
  One of the most well-studied plants to show rudimentary memory is the Venus flytrap. Native to the subtropical wetlands of the eastern United States, Venus flytraps have evolved the ability to obtain meat for sustenance, likely due to the lack of nitrogen in the soil. This is done by two trap-forming leaf tips that snap shut once triggered by a potential prey. On each lobe, three trigger hairs await stimulation. In order to maximize the benefit-to-cost ratio, the plant enables a rudimentary form of memory in which two trigger hairs must be stimulated within thirty seconds in order to result in trap closure. This system ensures that the trap only closes when potential prey is within grasp.
  
  The time lapse between trigger hair stimulations suggests that the plant can remember an initial stimulus long enough for a second stimulus to initiate trap closure. This memory is not encoded in a brain, as plants lack this specialized organ. Rather, information is stored in the form of cytoplasmic calcium levels. The first trigger causes a subthreshold cytoplasmic calcium influx. This initial trigger is not enough to activate trap closure, so a subsequent stimulus allows for a secondary influx of calcium. The latter calcium rise superimposes on the initial one, creating an action potential that passes threshold, resulting in trap closure. Researchers, to prove that an electrical threshold must be met to stimulate trap closure, excited a single trigger hair with a constant mechanical stimulus using Ag/AgCl electrodes. The trap closed after only a few seconds. This experiment demonstrated that the electrical threshold, not necessarily the number of trigger hair stimulations, was the contributing factor in Venus flytrap memory.
  
  It has been shown that trap closure can be blocked using uncouplers and inhibitors of voltage-gated channels. After trap closure, these electrical signals stimulate glandular production of jasmonic acid and hydrolases, allowing for digestion of prey.
  
  Many other plants exhibit the capacity to remember, including Mimosa pudica. An experimental apparatus was designed to drop potted mimosa plants repeatedly from the same distance and at the same speed. It was observed that the plants' defensive response of curling up their leaves decreased over the sixty times the experiment was repeated. To confirm that this was a mechanism of memory rather than exhaustion, some of the plants were shaken post experiment and displayed normal defensive responses of leaf curling. This experiment demonstrated long-term memory in the plants, as it was repeated a month later, and the plants were observed to remain unfazed by the dropping.