OTHER ACTIVITIES OF AUXINS 229 



been carried out with pure auxins, but there seems no 

 reason to doubt the identity. In this case we have a com- 

 bination of the growth-promoting effect with another effect 

 resulting in flower fall, the mechanism of which is as yet 

 unknown. 



We have seen that the auxins play a protean role in the 

 development of plants, and influence a large number of 

 processes, both normal and pathological. It is important 

 to note that, as discussed in Chapters VIII and XII, in 

 all cases investigated a substance which shows one of the 

 effects of auxin shows them all. Its acti\dty may some- 

 times be concealed, as in those substances which cause no 

 Avena curvature, or which produce root formation only 

 locally, but it may be demonstrated by special experiments. 

 Many of the apparently different effects are to be traced 

 to different types of cell enlargement, but others, such as 

 root formation, are more complex. It is difficult to avoid 

 the conclusion that ''all these functions arise from one 

 primary reaction in the cell; which physiological effect is 

 produced depends upon the nature and position of the tis- 

 sues affected. The actual primary reaction becomes, then, 

 of greater interest than ever. It is a kind of master reaction 

 governing the activities of the cell." So far as attempts 

 have been made to analyze further the nature of this pri- 

 mary reaction, they have been summarized in Chapter VIII. 

 It remains now to consider the role of auxin in comparison 

 with some other aspects of growth and development. 



