436 



PLANT PHYSIOLOGY 



through cauterization or pinching, will result in a rather rapid 

 transmission of the stimulus throughout the plant. As the 

 reaction wave spreads through the branch, the leaves will close 

 one after the other. This wave may be transported from 

 one branch to another and thus finally will involve the whole 

 organism. 



If the temperature is sufficiently high, above 25 to 30°C., then 

 the leaves of Mimosa will fold within a few seconds. Under these 



Fig. 137. 



-Mimosa branch. On the left, two open leaves. On the right, a leaf 

 lowered and folded, due to irritation {after Nathansohn). 



conditions, the stimulus received is also transmitted with great 

 rapidity, as fast as 15 mm. per second. Such an extremely 

 rapid response is not characteristic of plants in general. Natur- 

 ally then, Mimosa, which was first brought to Europe from 

 Brazil in the seventeenth century, very soon became widely 

 knowTi not only in scientific circles, but among the pubUc as 

 well. The sensitivity of this plant is very much akin to the 

 irritabiUty of animals. It may be suppressed either by lowering 

 the temperature to below 15°C., or by various anesthetics, 

 especially the vapors of ether or chloroform. 



What seismonastic sensitivity really consists in has not yet 

 been discovered. The only thing so far established is that it is 



