Physiological and Anatomical Effects 121 



longiflorum var. eximium Nichols) responds chiefly by proliferation 

 of the epidermis (Beal, 1938). 



Leaf Effects 



The most common immediately observable response to auxins 

 applied to foliage of plants is the development of epinasty; that is, 

 the downward curling and bending of leaves occasioned by swelling 

 of cells, particularly those on the dorsal sides of veins. In some cases 

 the leaves bend upward, which is known as hyponasty. Figure 51 



Fig. 54. Epiiiastic responses of tomato induced by naphthaleneacetic acid; left, 

 untreated control, center, NAA sprayed upon the foliage, and right, NAA solution 

 injected in stem (Zimmerman and Wilcoxon, 1935). 



shows some typical epinastic cinling and epinastic distorticjn of leaf 

 outline in tomatoes sprayed with 2,4-D. Epinasty is not strictly an 

 auxin function, for many poisons which inhibit cell enlargement can 

 also cause epinastic responses. These are discussed in more detail in 

 chapter VII. 



As in the case of stems, leaves too will differ in their responses 

 from species to species and will also differ with the growth regulator 

 used. For example, 4-chlorophenoxyacetic acid produces extensive 

 epinasty in tobacco and Kalanchoe leaves, whereas 2-chlorophenoxya- 

 cetic acid produces relatively little or none. Yet these two auxins 



