T. C. ALLEN 413 



of leaves in witches'-broom fashion at the internode. Many abnormal 

 tissue responses have been pointed out (8,12,17) showing that the feeding 

 of certain Empoasca species will cause stunting, rosetting, and prolifera- 

 tion of dwarfed shoots. Carter (3) observes a close analogy between the 

 development of adventitious buds and insect galls and suggests that a 

 possible relationship may exist between gall, hosts, and hormones. The 

 statement by Carter that "insects feed on a specific plant species only" 

 would suggest that auxin relations may be involved between insects 

 and plants. It was also his opinion that if symptoms following certain 

 insect feeding are "much more rapid than that of fungus or bacterial 

 infection, this appears to be the principal support for the numerous 

 susgestions in the literature that the secretions are toxic." 



That the feeding of Lygus upon potato stems indicates systemic 

 response or diffusion of a toxic principle in association with the feeding 

 of the insect has been reported by Leach and Decker (13). Smith (23) 

 concluded that when certain insects feed they inject toxic secretions 

 into plants and that the saliva of Miridae is so toxic it may cause 

 changes in the tissue much more rapidly than could be produced by a 

 virus. This speed of action is similar to that of applied hormones, and 

 the similarity is of considerable interest. 



Similarity in Enzymic Activity where it Appears hivolved. — Although 

 the specific action of auxin may still remain to be demonstrated, there are 

 good indications that auxin release and action are exerted in connection 

 with enzymes. 



Numerous investigators have pointed out the presence of enzymic 

 activity in connection with insect feeding upon plants. Cosens (4) in 

 considering the physiology of gall formation concludes that a larva 

 secretes an enzyme which converts starch to sugar. Typical lesions caused 

 by cotton flea hoppers were obtained by Painter (20) following injection 

 of diastase in plant tissue, and froghopper injury to sugar cane has been 

 shown to increase the content of oxidizing enzymes (10). Herford has 

 reported that certain leaf hoppers secrete diastase and invertase (11); 

 and Andrew pointed out that the saliva of some mosquitoes contains 

 an enzyme which produces a reaction in plant juices causing precipita- 

 tion of its contents (i). 



Little information is available, however, on the effect of enzyme 

 activity, insect feeding, or plant auxin on the growth and differentiation 

 in plants. Studies by Wildman and Gordon (26) show that proteolytic 



