186 PHYTOHORMONES 



by Went (1929); the buds strongly, and the leaves less 

 strongly, promoted formation of roots. In these experiments 

 distinction was made for the first time between number and 

 elongation of the roots. Debudded and defoliated cuttings 

 formed very few roots, or under some conditions none.^ If, 

 however, the diffusate from Papaija leaves were mixed with 

 agar and appHed to the cutting, an increase in the number 

 of roots was observed. Still greater increases were subse- 

 quently obtained by the application of diastase (which was 

 also active after being boiled) or of extract of rice polishings 

 (Bouillenne and Went, 1933). However, Gouwentak and 

 Hellinga (1935) were afterwards unable to obtain rooting by 

 the application of diastase. Sugar solution was found to 

 have no root-forming effect, so that the action is not one 

 of nutrition. Bouillenne and Went (1933) found that the 

 action of the extracts is exerted only at the base of the 

 cutting, and inversion with respect to gravity did not alter 

 this polarity; it was therefore deduced that "the polar 

 locaUzation of new roots is caused by the polar transport" 

 of the hormone. The formation of roots in seedlings is 

 closely comparable; if the roots are removed from the base 

 of Impatiens hypocotyls then the formation of new roots 

 is greatly promoted by the presence of the cotyledons or, 

 in the light, by leaves. The application of sugar to the 

 hypocotyl base in these experiments increased the number 

 of roots formed, but the cotyledons were necessary as well; 

 there is therefore a differentiation between hormonal and 

 nutritive factors, the influence of the cotyledons being ex- 

 plained as due to storage of root-forming hormone in them. 

 It follows from these experiments that root-formation is due 

 to a special substance or hormone (which Bouillenne and 

 Went named "rhizocahne"); it is not itself a nutrient, is 

 thermo-stable and is produced by leaves in the light. It is 

 also stored up in cotyledons and buds, and its transport is 

 basipetally polar. 



1 Graham and Stewart (1931a) subsequently obtained good rooting on isolated 

 Acalypha leaves. 



