414 PLANT GROWTH SUBSTANCES 



enzymes, such as tryptic extracts, trypsin, or chymotrypsin, release 

 active auxin from isolated plant protein preparations. An effect on 

 the plant protein resulting from insect feeding has been found by Smith 

 (22), who has shown that proteins and amino acids, as determined by 

 color tests, make up a major portion of the sheath material after certain 

 insect feeding. 



Suppression of Blossom and Pod Drop Caused by Lygus Species. — 

 A similarity in the action of hormones and of insects upon plants was 

 recently shown by the use of a-naphthaleneacetic acid to inhibit ab- 

 scission of blossoms and bean pods caused by the feeding of Lygus 

 oblineatus Say (7). Under field conditions the application of naphthalene- 

 acetic acid has resulted in greater retention of number of small bean 

 pods thereby improving the quality of the bean for market purposes. 



An explanation of the above behavior may be proposed as follows. It 

 is known that auxin inhibits leaf abscission (14). Possibly, therefore, 

 the insect feeding stops the normal auxin supply to the base of the petiole 

 thus permitting the abscission layer to form. The appUcation of a-naph- 

 thaleneacetic acid would then restore the normal supply of hormone and 

 prevent the abscission. The insect therefore may produce an auxin inac- 

 tivator or interfere in some other way with the normal supply. 



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