20 



REGENERATION 



twelfth day. Both leaves produced tiny roots in almost all 

 notches, both in air (la, Fig. 19), and in water (I, Fig. 19). 

 This, however, soon changed, as Fig. 20 shows, which was drawn 

 of the same two leaves 6 days later (Mar. 1). Leaf I, the apex 

 of which dipped into water, produced rapidly growing shoots 

 and roots in water, and the roots formed in the beginning in the 

 upper notches of this leaf had already dried out and soon dis- 

 appeared; the shoots in the notches some distance from the water 

 had also stopped growing (I, Fig. 20). In the other leaf, (la, 

 Fig. 20) which was entirely in air, all the roots still continued 

 to grow and also a number of shoots, but much more slowly than 



Apex in water 



Fig. 20. — Same leaves as in Fig. 19, drawn 6 days later. In leaf I, the roots 

 and shoots continue to grow only in the notches in or near the water while those 

 farther away from the water dry out. In leaf la, the roots and shoots in all 

 the notches still continue to grow. 



those at the apex of the other leaf. It is, therefore, obvious that 

 the wilting of the air roots of leaf I, the apex of which dipped 

 into water, must have been due to the fact that the more rapid 

 growth of the shoots and roots in the notches under water 

 attracted all or most of the sap of the whole leaf to these notches, 

 thereby preventing the growth in the other notches and causing 

 the air roots already formed in these notches to wilt. These 

 results are quite general, the only variation being that when the 

 leaf is small or less fleshy the roots and shoots may from the 

 beginning be more exclusively confined to that part of the leaf 

 which dips into water. When the leaf is entirely in air, roots and 

 shoots grow out in almost all the notches, but the growth is 

 always slower than in the notches dipping into the water. 



It is therefore a general rule that the more rapidly growing 

 notches of a leaf will attract all or almost all the sap from the 



