70 PHYTOHORMONES 



it is capable of growth. We must therefore envisage the 

 plant as furnished with certain spots or areas, each of which, 

 by virtue of precursor storage or supply, or presence of the 

 proper enzyme system, can produce auxin for a time. Gen- 

 erally the production ceases after a while, but in the mean- 

 time if these spots or areas are, like buds, capable of growth, 

 they will grow. Since, however, a very little auxin can bring 

 about a great deal of growth (10-*^ mg. can produce about 

 half a centimeter of coleoptile, as shown in III D \), it 

 follows that many of these centers will produce auxin more 

 rapidly than they can use it up, and thus auxin will diffuse 

 out of them into other parts. Auxin, then, is not produced 

 as a result of growth, but, rather, the auxin which enters 

 our experimental agar blocks is the excess over that which 

 has been used in growth. Auxin production is thus the 

 primary, and growth the secondary, phenomenon. A similar 

 conclusion was reached by W. Zimmermann (1936). 



D. Auxin in Animal Material 



The experiments of Seubert (1925) showed that auxin 

 may be present in considerable concentrations in saliva and 

 pepsin, both animal secretions. Systematic examination of 

 animal excretions and tissues was made by Kogl and Haagen 

 Smit (1931) and Kogl, Haagen Smit, and Erxleben (1933, 

 1933a) ; in the dog, most tissues contain very small amounts, 

 the kidneys, the urine, and the colon and its contents having 

 the most ; human urine, however, was found to be extremely 

 rich in auxin and was in fact used for the isolation of pure 

 auxins (see VII B). Maschmann (1932) and Maschmann 

 and Laibach (1932, 1933) found the Hver and kidneys of the 

 mouse and hen to be higher in auxin than other tissues. 

 According to Maschmann (1932) and to Kogl, Haagen Smit, 

 and Tonnis (1933) the auxin content of human carcinomas 

 is higher than that of the surrounding tissue. The authors' 

 own experiments did not show any particularly high auxin 

 content in rapidly growing mouse carcinomas (u). There 

 is no reason to ascribe any physiological significance to the 



