OTHER ACTIVITIES OF AUXINS 225 



however, do not bear this out, nor could Jost and Reiss 

 (1936), nor the authors (u), confirm it. It is true that the 

 place of apphcation of auxin is in some cases important for 

 its efTect; this is shown in roots (Chapter IX) and also 

 for the elongation or inhibition of stem growth (Le Fanu, 

 p. 214). Czaja's theory, discussed in VI D, that the polarity 

 of cells and tissues is caused by the direction of the prevail- 

 ing auxin stream was based upon these experiments. Went 

 (1936) has suggested a mechanism for the formation of 

 swellings in terms of the interaction between auxin and 

 other factors. 



The formation of callus at the base of a cutting is often, 

 though not always, associated by gardeners with good root- 

 ing of the cutting. In the hght of the above, it is probable 

 that a cutting which forms much callus does so because it 

 is rich in auxin, and the root formation is then due to the 

 auxin; the roots are not as a rule formed from the callus, but 

 both result from the same internal cause, namely the auxin. 

 The many exceptions to this rule pro\dde further evidence 

 of the role of other, non-auxin, factors in both processes. 



The auxin swellings bear a close resemblance to the 

 phenomena observed in some of the galls and other path- 

 ological outgrowths, and there is good evidence that auxin 

 plays an important part in such growths. The root nodules 

 of leguminous plants are active auxin-forming centers when 

 still growing, and their initiation and growth are almost 

 certainly due to the auxin produced by the invading bac- 

 teria (Thimann, 19366; cf. IXC). These can therefore be 

 considered as root-galls, arising by pathological swelling 

 of a lateral root initial. The crown-gall organism, Pseudo- 

 monas tumefaciens, also produces auxin, since Brown and 

 Gardner (1936) have obtained typical swellings and out- 

 growth by extracts from cultures of this bacterium (see 

 also Duyfjes, 1935). They have also produced large galls 

 on Phaseolus by long-period application of pure indole- 

 acetic acid at a cut surface (see Figure 61). The experiment 

 of Nemec (p. 187) also indicates auxin production by this 



