GENERAL CONCLUSIONS 235 



the effect of increasing the growth and development of a 

 number of different plants. This is shown by increased 

 production, dry weight, etc., in wheat, rye, barley, beans, 

 and sugar-beets (Scharrer and Schrop, 1935) and tomatoes 

 (Schoeller and Goebel, 1935). The effect can be ascribed 

 to a stimulation of the earlier growth stages. Stimulation 

 of flowering, either by an increase in the number of flowers 

 or by the earlier opening of the first flowers, has also been 

 reported (Schoeller and Goebel, 1935). This also seems to 

 be correlated with better growth. The experimental condi- 

 tions necessary to obtain positive results are of great im- 

 portance, since various investigators were unable to confirm 

 Schoeller and Goebel's earlier work (1931-1934) {e.g. Harder 

 and Stormer, 1934; Virtanen, Hansen, and Saastamoinen, 

 1934). Indications that oestrone has an effect on root forma- 

 tion are mentioned in XI E. 



Comparison has recently been made between the phe- 

 nomena of crown-gall disease and animal cancer (Levine, 

 1936). This comparison, which was first made 20 years 

 ago by E. F. Smith, rests upon very superficial similarities 

 and appears quite unjustified. Conversely, little comparison 

 can be drawn between the auxins and the animal carcino- 

 genic substances. These substances, which are hydrocarbons 

 (see Fieser, 1936), are very slow in acting, and it seems 

 probable that their effect is to induce normal cells to change 

 into cancerous cells rather than to promote cell growth 

 directly. 



C. Comparison with Growth Substances of 

 Lower Plants 



In contrast to the above true hormones stand the growth 

 promoting substances for fungi and microorganisms. While 

 free movement of these substances may take place within 

 the organism it is not an essential part of their acti\dty; 

 this is particularly obvious for unicellular microorganisms, 

 in which correlations as ordinarily understood cannot occur. 

 While microorganisms, therefore, cannot, by definition, have 



