94 



REGENERATION 



We have seen that when a piece of defoliated stem is suspended 

 in moist air with its base in water shoot formation commences 

 in a few days in the most apical nodes and the apical shoots grow 

 rapidly. When, however, the piece of stem of a plant less than 

 one year old is defoliated, leaving only a pair of leaves at the apex 

 (Fig. 71), and if the stem is suspended vertically, roots are formed 

 in abundance at the base but all the shoot formation in this 

 stem is suppressed for a long time if not indefinitely. The draw- 



( !4 



U 



Fig. 69, Fig. 70. 



Fig. 69. — Diagram showing arrangement of shoot buds in the stem of Bryo- 

 phyllum calycimim. The line connecting the two buds in one node is always 

 at right angles to the line connecting two buds in the next node. 



Fig. 70. — Diagram explaining the inhibitory influence of the descending sap 

 from the apical leaf on shoot formation in the stem. The region of the stem 

 reached by the sap from the apical leaf is shaded, and in the shaded part regen- 

 eration of shoots is inhibited. 



ing was made after 6 weeks, but the situation had not changed in 

 the next month when the experiment was discontinued. One 

 stem in six finally formed a shoot in the axil of one of the apical 

 leaves and one in the fourth node below the apical leaves. This 

 experiment shows that the descending sap from a leaf favors root 

 formation but suppresses shoot formation in the basal part of a 

 young stem. This fact is also shown in the following experi- 



