Learning from nature : experimental observation of mimosa pudica

Abstract

In the plant kingdom, there exists an interesting phenomenon–rapid plant movement. For example, some Orchids can explosively disperse pollinium to increase cross reproduction. Venus flytrap is able to rapidly snap the lobes to catch the visiting insects to obtain nutrients. Mimosa pudica is famous for its fast leaf-closing movement to defend against predators. Generally speaking, fast movements in plants are the result of natural selection that requires plants to have an immediate response to the external stimuli. Unlike animals, plants do not have muscles to generate such rapid movements. Therefore, the question of how plants are able to move rapidly in the absence of muscle has aroused researchers’ huge interest. Recent pioneering work has interpreted the rapid plant movement in light of the physical perspective, including water-driven movements and snap-buckling instability. Especially, Mimosa pudica has become a popular model to study the rapid plant movement, due to its well-known natural history; easily obtainable and maintained; fast germination rate; and observable leaf-closing properties. This study aimed to investigate the rapid movement of wild Mimosa pudica upon mechanical stimulation by hand touch. In this study, the relationship between various dimensions of 50 wild mimosa samples and the response time upon stimulating the full pinna area was firstly explored. Then, to investigate the effect of the reduced stimulation contact area on the response time, another experiment by only stimulating 1/3 of the pinna tip was further performed on 50 wild mimosa samples. Next, the fatigue effect of Mimosa pudica after consecutive stimulations was investigated. Lastly, Box & Whisker plot was employed for data analysis. A box plot depicts groups of numerical data graphically through the five-number summary. The five-number summary includes: the minimum (0th percentile or Q0), the first quartile (25th percentile or Q1), the sample median (50th percentile or Q2), the third quartile (75th percentile or Q3), and the maximum (100th percentile or Q4). As for the entire pinna stimulation, the results suggested that there was no significant relationship between the closing time and various mimosa dimensions. However, a steadily decreasing trend was demonstrated between the reopening time and pulvinus diameter, indicating that the greater pulvinus size tended to have a shorter reopening time. Besides, the fatigue effect was only exhibited with respect to the reopening time, by means of increasing the reopening time and refusing to open with greater stimulation cycles. Whereas closing time did not show any sign of fatigue effect. Further, the partial pinna stimulation results displayed analogous trendlines compared with entire pinna stimulation, in respect to closing/reopening time versus various mimosa dimensions as well as fatigue effect. Remarkably, the partial pinna stimulation demonstrated a twofold increase in closing time in comparison to entire pinna stimulation, which implied the stimulation contact area did play a significant part in pinna closing time but had no effect on pinna reopening time. This study would contribute to the advancement in the areas of robotics and microfluidics. Moreover, by studying the motor organs of Mimosa pudica that are responsible for the fast movement, it would also inspire researchers with the design of actuators.