Plant arithmetic is a form of plant intelligence whereby plants appear to perform arithmetic operations – a form of number sense in plants. Some such plants include the Venus flytrap and Arabidopsis thaliana.
Arithmetic by species
Venus flytrap
A closing trap
The Venus flytrap can count to two and five in order to trap and then digest its prey.[1][2]
The Venus flytrap is a carnivorous plant that catches its prey with a trapping structure formed by the terminal portion of each of the plant's leaves, which is triggered by tiny hairs on their inner surfaces. A Venus flytrap's reactions can occur due to electric and mechanical, or movement-related, changes.[3][4][5] When an insect or spider crawling along the leaves contacts a hair, the trap prepares to close, snapping shut only if a second contact occurs within approximately twenty seconds of the first strike. The requirement of redundant triggering in this mechanism serves as a safeguard against wasting energy by trapping objects with no nutritional value, and the plant will only begin digestion after five more stimuli to ensure it has caught a live bug worthy of consumption.
There are two steps, which are a closed and locked state, that a Venus flytrap undergoes after its open state and before digestion, which differ due to the formation of the trap.[3][4][5] A closed trap occurs when the two lobes close or catch prey.[3][4][5] A locked trap occurs when the cilia further trap the prey.[3][4] The trap can possess a strength of four newtons.[4] In addition, the cilia can further hinder a creature's ability to escape.[3][4]
The mechanism is so highly specialized that it can distinguish between living prey and non-prey stimuli, such as falling raindrops;[6] two trigger hairs must be touched in succession within 20 seconds of each other or one hair touched twice in rapid succession,[6] whereupon the lobes of the trap will snap shut, typically in about one-tenth of a second.[7]
The number of days that the trap remains closed will depend on whether or not the plant has caught prey.[3] Furthermore, the size of the prey can affect the number of days needed for digestion.[3] If a creature is too small, then the Venus flytrap has the ability to release it, which means that it can start the stage of becoming semi-open.[3][4] The transition from closed to open will take two days and can result after the plant has finished digesting or realizing it has not caught anything worthwhile.[3][4] One day will be needed to become semi-open, which creates a concave look, and the other day will allow the Venus flytrap to become fully open, which creates a convex look.[3][4] The angle of a Venus flytrap's lobes when they are open can be impacted by the water within it.[5]
Most plants accumulate starch by day, then metabolize it at a fixed rate during night time. However, if the onset of darkness is unusually early, Arabidopsis thaliana reduces its use of starch by an amount that effectively requires division.[9] However, there are alternative explanations,[10] such as feedback control by sensing the amount of soluble sugars left.[11] As of 2015, open questions remain.[12]
