86 



REGENERATION 



reaches primarily root-forming tissue, we should expect that the 

 tissue sap collecting on the lower side of a horizontally placed 

 stem should give rise only to roots but not to shoots, as it actually 

 does. 



Figure 64 shows the regeneration which occurs in stems sus- 

 pended horizontally in moist air. The upper stem is entirely 



Fig. 64. — Roots grow on under side of stems suspended horizontally, but 

 more roots grow when there is a leaf at the apex of the stem. Nov. 18 to Dec. 

 13, 1923. 



defoliated. It has formed shoots at the apex and roots on the 

 upper as well as on the lower side of the most basal, fifth node, 

 but more on the lower side. There are also a few roots on the 

 lower side in the fourth node and none on the upper. There is 

 only a slight indication of the influence of gravity on the growth 

 of roots. The geotropic curvature is only slight as it always is 

 in completely defoliated_stems. 



