No. 507] BOTANICAL SOCIETY OF AMERICA 155 



tween autonomous and induced or paratonic movements 

 was not so sharply drawn then as it is now. At present 

 we place the tropistic movements due to whatsoever exter- 

 nal cause, under the general class of aitonomic movements, 

 in contradistinction to circumnutation, epinasty, hypo- 

 nasty and so forth, which we are pleased to term auto- 

 nomic or due to internal causes. In the latter class, it must 

 be confessed, the relegation of movements to autonomous 

 causes is often a mere confession of ignorance, as is well 

 instanced by the older opinion first advanced by Darwin 

 that the twining of stem climbers is wholly autonomic. It 

 is only in the sense that the movements of fixed plant 

 organs are in the vast majority of cases ultimately due to 

 unequal growth changes that we can say that circumnuta- 

 tion is the fundamental process concerned. In other 

 words, it is only if we were to define circumnutation as the 

 power of plant parts to show either unequal turgescence 

 or unequal growth that we could accept the universality 

 of Darwin's statement. 



As far as his observations on circumnutation proper 

 are concerned, or, as he would have termed it, unmodified 

 circumnutation, his conclusions are of the highest value, 

 and form even to the present day really a large part of 

 our literature on the subject. By the simplest means 

 he plotted the orbits, so to say, of a very considerable 

 number of growing tips. Entirely aside from any 

 especial interpretation to be placed upon them, his de- 

 scriptions of the behavior of seeds during germination 

 and of the growth of seedlings, give a clear and accurate 

 account of the general organography of the adolescent 

 plant. 



In another very important direction were the researches 

 of Darwin rewarded by far-reaching results ; namely, in 

 the matter of the transmission of stimulus in plants. Un- 

 til the publication of his experiments it had been largely 

 overlooked that there might be a separation in space 

 between the percipient and motor zone in tropic re- 

 sponses. It is true, no doubt, that some of his methods 



