64 PLANT RESPONSE 



gravity. In the specimen of Mimosa (a) the maximum 

 responsive deviation of 25° was reached in a little more than 

 one second, after which occurred the peculiar reversal already 

 referred to. This, which was due to fatigue, was completed 

 in seven and a half seconds. The next curve (d) was ob- 

 tained from the young leaf of Citrus decumana. It will 

 be observed that here we have a practical duplication of the 

 curve of Mimosa, the only difference lying in the longer 

 period necessary for the completion of its different parts. 

 The responsive deviation in this case is 30°, that is to 



Fig. 33. Response of Leaves of Ordinary Plants to Electric Stimulation 

 The ordinate represents the angular movement in degrees. 



say, even greater than that of Mimosa. This was attained 

 in eleven seconds, and reversal completed in twenty five 

 seconds. The extent of these responsive movements, being 

 due to differences of excitability as between the two halves, 

 will, it is easy to understand, be modified by the age of the 

 leaf. This fact is illustrated by the next curve (r), obtained 

 with an older leaf of the same plant. Here the responsive 

 movement takes place through only 10°, and there is only a 

 partial reversal. 



The instances given may be considered as typical, the 

 responses obtained with specimens of other plants being 

 simply variations of these. For example, while some leaves 



