PLANT SCRIPTS 5 



has been observed in Spirogyra by Nageli and in Nitella 

 by Hofmeister. 



Whatever theory may be held, the undoubted fact in 

 these two cases, of plant and animal alike, is the occurrence 

 of a fundamental excitatory protoplasmic change which finds 

 external expression in alteration of form. If we now 

 record the responsive movement, we shall be recording" what 

 is an effect of excitatory change, either in plant or animal. 

 Whether or not this fundamental change is similar in the two 

 cases can only be decided by comparing the records due to 

 excitation, in plant and animal tissues, under all possible 

 variations of external conditions. 



The fall of the leaf of Mimosa is brought about in 

 consequence of the contraction of cells in the lower half 

 of the pulvinus. I shall for convenience describe the fall 

 as the contractile movement, in contradistinction to the 

 erectile movement brought about by the recovery of cells 

 into normal turgid and expanded condition. 



In studying the excitatory reactions of the plant, under 

 external stimulus, we have to determine, first, what time 

 elapses between the incidence of the shock and the initia- 

 tion of a perceptive responsive movement. This constitutes 

 the determination of the Latent Period. We have next 

 to find out at what rate this responsive movement of the 

 leaf takes place, and after what time the contractile phase 

 of the movement is exhausted. After a short pause 

 the plant gradually recovers from the effect of the shock, 

 and the leaf is re-erected to its former position. We there- 

 fore Want to know the various rates at which recovery 

 gradually takes place. In order to secure these data] it 

 will be necessary to make a graphic record of the entire 

 responsive movement of the plant organ. This record, 

 further, must furnish us not only with the amount, but also 

 with the time-relations, of this movement. This would 

 involve the construction of a writing-lever which, deflected 

 by the pull of the falling leaf, would be capable of tracing 

 on a writing-surface, moving at a known uniform rate, the 



