88 



REGENERATION 



in the internode between 2 and 3, abundant roots are formed 

 exclusively on the lower side. In order to prevent the stem from 

 undergoing too much curvature and from being thrown alto- 

 gether out of an approximately horizontal position, it was loosely 

 tied to a piece of wood as shown in the drawing. 



It can be shown that the mass of the roots formed in horizon- 

 tally placed stems increases with the mass of the apical leaf. The 

 two stems in Fig. 65 were suspended simultaneously, the lower 

 stem with a whole leaf at the apex formed more roots than the 

 upper stem with a leaf reduced in size (May 4 to June 5, 1923). 



Fig. 66. — Roots grow on under side of a stem suspended horizontally even when 

 the geotropic curvature of the stem is prevented. 



It can be shown quantitatively that the formation of air roots 

 in stems suspended horizontally increases with the mass of the 

 apical leaf. These experiments are not very accurate on account 

 of the small weight of the roots formed and on account of the 

 fact that air roots dry out and fall off, while new air roots are 

 formed. Table XX shows, however, that on the whole the mass 

 of roots formed increases with the mass of the apical leaves. 



In these experiments the stems bent geotropically and the 

 curvature increased with the mass of the apical leaf. This 

 might suggest the idea that the root formation on the under side 

 of the stem was not a direct effect of the collection of sap on the 

 lower side of the stem but an indirect effect and that it was pri- 

 marily due to the curvature. This, however, is not correct. 



