10 



Fundamentals of Auxin Action 



hormone flowing through the various plant parts in extremely minute 

 quantities (figure 1). 



We should remember that this picture of plant growth is limited 

 in completeness principally by our limitations of knowledge. We are 

 forced to interpret growth phenomena principally on the basis of 

 auxin functions largely because the auxin effects are the ones with 

 which we can experiment most eff:ectively and hence which we know 

 l)est. This may result in concepts somewhat biased toward auxin, as 



Auxin controls 



cell enlargement 



(stem, bud, leaf, root) 



Auxin controls 

 apical dominance ^ — ^^ 



When auxin flow 



ceases, abscission 



results (leaves, 



flowers, fruits) 



Auxin controls cell 

 and organ 

 differentiation 



Auxin affects 

 reproduction (flower 

 Initiation, development, 

 fruit -set, fruit growtt), 

 embryo growtt\) 



Auxin controls 

 direction of growtt) 

 (tropisms of 

 stems, roots ) 



Fig. 1. Diagrammatic representation of the auxin regime in plants. Auxin is 

 formed in the plant extremities and moves inward, as indicated by heavy arrows, 

 controlling an array of growth functions through the plant. 



Burstrom (1953) has pointed out, but until we know of more subtle 

 controlling influences, these concepts will stand as the most complete 

 descriptions of plant growth and development known. 



As time goes on, new research appears to be attributing more and 

 more physiological functions to the growth hormones in plants. The 

 magnitude of their influences on the physiology and anatomy of the 

 plant is undoubtedly still not fully recognized. 



THE AGRICULTURAL IMPACT 



The development of knowledge of the auxins has had a remark- 

 able effect on the agricultural sciences. Not only has it made possible 



