444 Spalding . — On the Tranmatropic 
and how, if proven, it is in the slightest degree inconsistent 
with the existence of both sensitiveness and induction does 
not appear. ‘Through lateral injury of the root-tip, the 
growing part of the root lying above the wound undergoes 
a change which results in greater ductility of the cell- 
membranes of this part.’ But changes in the membranes of 
growing cells are brought about through the agency of their 
protoplasm, and the protoplasm of these cells cannot fail to 
be affected by the treatment the root has received and to 
react in one form or another. Wiesner’s argument, therefore, 
does not affect the question of the sensitiveness of the root- 
tip, whatever bearing it may have upon the mechanics of 
growth-curvatures. 
The papers just reviewed contain all of importance that has 
been urged against the view held by Darwin regarding the 
sensitiveness of the growing point of the root. On the other 
hand, Pfeffer, after the most extended investigation that has 
yet been made of the mechanics of growing roots, states his 
conviction that the mechanical explanations thus far given are 
insufficient to account for the phenomena, and that they 
belong rather to movements of irritation ( Reizbewegungen 1 ). 
The question being thus reopened, the evidence derived from 
the present experimental study remains to be examined. 
As stated in the introduction, and shown in experiments i, 
2, and others, two distinct changes of form regularly follow 
lateral injury of the root-tip, one of which also follows when 
the root is wounded farther back. The latter, which in this 
paper is spoken of as the mechanical bend, results from 
structural and mechanical changes, and is to be clearly 
distinguished from the other (traumatropic) curvature, which 
is a proper growth-curvature 2 . 
1 Druck- und Arbeitsleistung, p. 374. 
2 As the present paper is limited to a consideration of the traumatropic curvature 
proper, no attempt is made to discuss further the mechanical bend, nor what 
Wiesner calls the Nebenkriimmung, which is referred by him to changes of 
turgor. Still other curvatures are seen when growing roots are continuously 
observed, and confusion will be avoided by confining the attention to the curvature 
which Darwin investigated. The term traumatropism proposed by Pfeffer should 
