2IO CLASSIFICATION 



few of the leaflets are touched. For example, if the 

 lowest leaflet of a secondary axis is touched, all the 

 leaflets of that axis fold upwards and forwards rapidly 

 in succession from the base to the apex. The stimulus 

 then proceeds to the next contiguous secondary axis, 

 which closes its leaflets in the same manner, and so on 

 to the third and fourth axes. The four secondary axes 

 then come closer together, and ultimately the primary 

 axis droops downwards. The stimulus, if sufficiently 

 strong, is often communicated to contiguous leaves, 

 which close in the same manner as above. The pul- 

 vinus seems to be the motor apparatus. The manner 

 and the rapidity with which the stimulus is conveyed 

 from leaflet to leaflet, from secondary axis to secondary 

 axis, from one leaf to another leaf, is similar in char- 

 acter to the conduction of nervous impulse in animals, 

 so much so that many physiologists are inclined to 

 believe that it is also a kind of nervous impulse con- 

 ducted in the same way in plants as in animals, 

 although the nervous mechanism has yet to be dis- 

 covered in plants. Recent researches of Sir J. C. 

 Bose seem to indicate that the sieve-tubes, with the 

 companion cells, are the main channels for the con- 

 duction of the nervous impulse in plants. 



Sir George Watt thus writes of the Sensitive Plant: 

 "The leaves of the Sensitive Plant close when you 

 touch them, and yet they do not do so when they 

 are made to touch each other by the wind. On the 

 approach of rain, the leaves prepare for a possible 

 storm by closing. If rain comes suddenly, the drops 

 on touching the leaves do not for a time cause them 

 to close, the plant being surprised. If you take a 

 Sensitive Plant (grown in a flower-pot) into your 

 carriage beside you, the leaves will close when the 

 carriage moves, but after a time they will open again 



