THE INFLUENCE OF GRAVITY 



91 



and that the polar character of regeneration in the stem of Bryo- 

 phyllum must therefore be due to the fact that in a stem sus- 

 pended upright and vertically the ascending sap flows in channels 

 which reach primarily the anlagen for shoot formation but not 

 those for root formation. 



Fig. 68. — Stems with leaves at the base and suspended horizontally form 

 roots apically from the leaf on the under side of the stem, but not on the upper 

 side, showing that the ascending sap from a leaf can form roots as well as shoots. 

 Dec. 16 to 27, 1923. 



When the stem is suspended vertically the tissue sap causes the 

 initial formation of roots in nodes above the basis which was 

 described in Chapter VIII. 



When a leaf is in the middle of a stem suspended horizontally 

 the main curvature occurs chiefly in the basal parts of the stem 

 as does also the root formation. 



This influence of gravity on the formation of roots in a stem of 

 Bryophijllum suspended horizontally is more pronounced when 



