116 Fundamentals of Auxin Action 



growth are secured only occasionally (Stier and du Buy, 1938; Tang 

 and Loo, 1940) and in many instances inhibitions alone follow the 

 treatment (Stewart and Hamner, 1942). A complete review of the 

 many studies of auxin treatments of seeds up to 1952 has been made 

 by Kruyt (1954), who concludes that a more profound understanding 

 of germination and of auxin action is needed before consistent re- 

 sults can be obtained. More jjrecise control of the environment 

 appears to yieltl more consistent etiects (chaptei' XIV). 



Cholodny (1936) pointed out that possibly the stimulation of 

 growth and development obtained by auxin treatments of seeds may 

 be related to the effects obtained by low temperatiue treatments, or 

 vernalization. The researches of Gregory and Purvis (1940) at London 

 have indicated tliai veinali/atioii is not a function of the growth 

 hormone. More recent evidence suggests that some sul)tle relationship 

 between auxin and vernali/ation may exist (Leopold and Guernsey, 

 1953). 



ANATOMICAL EFFECTS 



A voliuninous literatiue has accumulated on the subject of the 

 anatomical responses of various plants to the apjjlication of various 

 auxins. Perusal of the observations that have been made brings one 

 lo the realization that the responses which will be obtained depend 

 upon many factors l)oth in the environment and in the plant itself. 



Tissue Sensitivity 



The literature on anatomical and morphological responses to 

 applied auxins brings out three general factors which seem to have a 

 bearing on the responses obtained: 1) the degree of differentiation of 

 tissues in the plant when the application is made, 2) the formative 

 activity of the particular auxin used, and 3) the transport of the auxin 

 and its ultimate distribution through the plant. 



In regard to the degree of differentiation of various tissues as a 

 factor in the anatomical effects obtained, it would appear that tissues 

 which are least differentiated have the greatest potential for response 

 to an auxin or a growth regulator. Conversely, tissues which are highly 

 differentiated and matured are least responsive (Beal, 1951). Thus, if 

 one were to list the tissues of a stem in order of increasing degree of 

 differentiation one would find that in general the tissues highest on 

 the list (i.e. least differentiated) would have the greatest potential for 

 response, and with increasing degrees of differentiation, responsiveness 

 declines. A list of this sort might appear as follows: 



