254 THE ACTION OF THE LIVING CELL 



do not explain why the new growth follows. In other 

 words, given an adequate supply of the basic sub- 

 stances necessary for the formation of new plant tis- 

 sue, one must also account for their utilization in 

 the formation of new cells — that is, for the excitant 

 that leads to cellular multiplication at the site of 

 injury. 



In our discussion of the tropistic responses of plants 

 we have seen that injury apparently leads to the liber- 

 ation of a growth-promoting substance, presumably 

 derived from the injured cells. Hence one is tempted 

 to postulate that it is such a substance which is liber- 

 ated from mutilated tissue that leads to regeneration 

 at the site of injury. The accretion of sap at this point 

 would tend to hinder the diffusion of the growth ex- 

 citant from the site of injury, and thus permit the 

 neighboring cells to receive the full brunt of its ac- 

 tion. This is, of course, only speculation ; but it should 

 be capable of experimental test in some fashion. 



In view of these conclusions it is of interest to recall 

 the early observations of Jost ( 1 893 ) , who found that 

 if potatoes were injured in close proximity to the 

 eyes, germination was accelerated. A similar end was 

 achieved by Schneider (1925) by the simple expedi- 

 ent of inserting near the eyes sticks coated with various 

 chemicals. Schlumberger (1926), in a reinvestiga- 

 tion of this curious phenomenon, came to the conclu- 

 sion that the chemicals employed by Schneider were of 

 little or no consequence, the accelerated germination 

 being due to the trauma incident to the insertion of 

 the sticks into the potatoes. In conformance with this 

 conclusion, Schlumberger found that a simple me- 

 chanical jolting, or the application of pressure to seed 



