22 



REGENERATION 



It is obvious that the leaves suspended in air form a much 

 smaller quantity of dry weight of shoots and roots per gram of 

 dry weight of leaf during the same time and under the same condi- 

 tions than the leaves dipping into water. Hence, if we accelerate 

 the growth of some notches in the leaf, e.g., by dipping them into 

 water, we thereby inhibit the growth in the other notches. 



When leaves are suspended entirely and permanently in air, 

 practically all the notches commence to form shoots and roots 



Fig. 22. — Leaves with purplish pigment. The pigment from the whole leaf 

 migrates to the notches where new shoots are growing. 



(see Fig. 20), but not all will continue to grow. Some notches 

 will grow more rapidly than others and all the material will flow 

 to the more rapidly growing notches. This explains why ulti- 

 mately only a limited number of notches will continue to grow in 

 air, usually in the more fleshy parts of the leaf (leaf to right in 

 Fig. 21). 



The fact that the sap available in a leaf flows to those notches 

 where the growth is most rapid can be seen directly in leaves 

 which form a purplish pigment (probably anthocyanin). This 

 occurs only in leaves of Br-yophyllum suspended in air, not in 

 leaves which dip into water. Figure 22 shows two leaves of this 

 kind suspended in moist air. The experiment lasted from Feb. 



