CHAPTER V 



THE INFLUENCE OF GRAVITY ON THE FORMATION OF 

 ROOTS AND SHOOTS IN A DETACHED LEAF OF 



BRYOPHYLLUM 



The rule discussed in the preceding paragraph that all the sap 

 of a detached leaf flows to those notches where the growth is 

 more rapid explains in a simple way one of the mysterious 

 phenomena in the regeneration and growth of plant organs; 

 namely, the influence of gravity on regeneration. 



This influence can be demonstrated and studied in leaves of 

 Bryophyllum which are suspended entirely in air in a vertical 



Fig. 23. — Influence of gravity on formation of roots and shoots in leaves 

 suspended sidewise and in a vertical plane in moist air. Roots and shoots are 

 formed only on the lower edge of the leaf. 



plane and sidewise (Fig. 23). In this case shoots and roots 

 develop chiefly or exclusively on the lower edge of the leaf, not 

 on the upper edge. This is a striking and universal result. 

 (The figure was drawn on the eighteenth day.) It can be shown 

 that roots and shoots can develop also on the upper side of such 

 a leaf; all that is necessary for this purpose is to cut off the lower 

 edge of leaves suspended sidewise in moist air. In this case, a 

 vigorous development of shoots takes place in the upper notches 

 of the leaf. The two leaves in Fig. 24 are sister leaves, both 

 suspended vertically and sidewise in moist air. The leaf on the 



24 



