120 Fundamentals of Auxin Action 



paste to the leaf bases of intact bean plants produced extensive growth 

 abnormalities over the entire |)hint, particularly in areas directly basi- 

 petal to the point of apj^litation. If application of the same material 

 was made on decapitated beans, translocation was very much retarded 

 in the absence of the leaves. The usual extensive growth abnormal- 

 ities over the plant were not observed. Instead, a great local swelling 

 occurred on the stem near the point of application and from this 

 swelling there emerged great numbers of adventitious roots. 



Gustafson (1941) reports another instance of the distribution of 

 auxin affecting the morphological response obtained. He applied 

 phenylacetic acid to young bean seedlings. This auxin is transported 

 in plants only with great difficulty (Thimann and Schneider, 1939). 

 Whereas 2,4-D causes distortions all the way to the base of the plant 

 and causes as well the inhibition of lateral buds, phenylacetic acid 

 was found to produce only a local callus-like growth in the vicinity of 

 the application. Bud inhibition was notably absent. It seems fair to 

 assume that such differences between auxins may be accounted for on 

 the basis of the simple susceptibility of the auxin to translocation in 

 the plant. 



One rather startling effect of auxins on stem growth is the destruc- 

 tion of the primary phloem, brought about by the active proliferation 

 of the young phloem cells or of parenchyma adjacent to the phloem 

 (Eames, 1950). Since large quantities of auxin are transported in the 

 phloem, it is hardly surprising to find that the phloem responds quite 

 generally to auxin sprays by rapid proliferation, even though phloem 

 cells are generally more differentiated and less sensitive to auxins than 

 some other tissues. In cases where the phloein is actually destroyed by 

 proliferation, Eames points out that the capacity of the plant to survive 

 may be very seriously impaired, and so this phenomenon may account 

 in part for the herbicidal effects of auxin sprays. Struckmeyer (1951) 

 has made the interesting suggestion that the susceptibility of dicotyle- 

 donous plants to auxins may be due in part to the presence of cells 

 in and about the phloem which are only weakly differentiated and 

 hence capable of proliferation. In the resistant monocotyledonous 

 plants, on the other hand, the phloem is usually surrounded by 

 highly differentiated fibrous cells which are much less responsive to 

 auxins. 



The responses of stems to auxin applications vary somewhat from 

 species to species. Among the lilies, for example, it has been reported 

 that the white trumpet lily (L. longiflorum, Thunb.) responds to 

 indoleacetic acid principally by proliferation of parenchyma adjacent 

 to the vascular bundles, whereas the closely related Easter Lily (L. 



