THE GROWTH OF ROOTS 147 



(1936). The most basal zones of roots 60 mm. long or so, 

 however, transported practically no auxin in either direc- 

 tion. The velocity of movement was about 4 mm. per hour. 

 JMagao (1936) found in Vicia Faba, on the other hand, that 

 the auxin diffusing out from cylinders taken from near the 

 tip was greater from the basal than from the apical surface. 

 In an experiment of Cholodny (1934), coleoptile tips were 

 applied to the apical or the basal cut surface of decapitated 

 roots; if these were then placed horizontally, the stumps 

 with tips on their apical ends curved geotropically, the 

 others not. He concluded that auxin moved only basipetally 

 in the root, although Heidt's very similar experiment with 

 Sinapis alba indicated movement in both directions. That 

 some transport certainly takes place from base to apex is 

 shown by the experiments of Thimann (1936a) on the 

 formation of lateral roots of Pisum by auxin applied to the 

 stump of the shoot (see XI F). He also found that auxin 

 applied to the scutellum of Avena greatly inhibited the 

 growth of the young roots, and if applied at the base of the 

 shoot in older plants it here also — though to a lesser extent — 

 inhibited the growth of the roots. Transport from base to 

 apex in Avena roots therefore probably decreases with age. 

 Such experiments on roots are made more difficult by the 

 rapid destruction of auxin which takes place (Gorter, 1932; 

 Fiedler, 1936), but there seems no doubt that transport in 

 both directions occurs in Pisum, Zea, Avena, and Vicia, al- 

 though doubtless the ratio of the transport intensities in 

 the two directions varies. 



An interesting feature of the action of auxin on roots is 

 its production of swellings. Cholodny (1931a) showed that 

 when 3 maize coleoptile tips, instead of one, were applied 

 to the root stump there was a marked swelling in the growing 

 zone. This swelling was mostly confined to the cortical 

 parenchyma. Bouillenne and Went (1933) noticed that 

 cuttings on which leaves had been grafted, and which rooted 

 \'igorously, frequently gave abnormal thickenings near the 

 root tip, doubtless due to the excess of auxin coming from 



