214 PHYTOHORMONES 



growth produced by the auxin. However, this hypothesis 

 was satisfactorily dismissed by Skoog and Thimann (1934) 

 because in their experiments inhibition was complete with- 

 out any noticeable growth increase at the top of the stem. 

 This can be shown very clearly in peas by the inhibition of 

 the bud in the axil of the cotyledon. Also, in Figure 59 

 the enormous bud development of the controls obviously 

 represents more growth than the shght stem swelling in the 

 auxin-treated plants, whose buds are completely inhibited. 



Le Fanu (1936) has brought to light some interesting new 

 facts in connection with the inhibition. She found, firstly, 

 that the application of dilute solutions of indole-acetic acid 

 to the base of stem sections of Pisum inhibited their elon- 

 gation ; if lanoline paste was used, the auxin paste decreased 

 the growth when applied at the base, although (under some- 

 what different conditions) the same concentration increased 

 the growth when apphed to the apex. These results resemble 

 those of Faber (1936) and Thimann (1936a) on roots, in 

 which the effect of auxin also depended on its point of appli- 

 cation (c/. IX D), and they indicate that the effect of auxin 

 on an organ may be determined by whether it has to move 

 with or against the normal polarity. In the second place 

 she showed that in plants with two nearly equal shoots, the 

 shorter, which was being inhibited by the longer, yielded 

 only traces of auxin to agar, while normal shoots under the 

 same conditions yielded 26 units in 3 hours. Sections of the 

 inhibited shoot also transport practically no auxin through 

 them, whether it is applied apically or basally. Le Fanu 

 concludes that this evidence is against the view that the 

 shoot can be inhibited by the direct entry of auxin into it, 

 and supports rather the concept of some indirect means of 

 inhibition. However, it is clear that the inhibition of stem 

 sections by auxin at the base seems to be comparable to the 

 inhibition of one shoot or bud by another which supplied 

 auxin to its base. 



In the hope of elucidating the mechanism of inhibition 

 Went (1936) has attempted to assess the role of the other 



