Regeneration 



161 



cells which give rise to legs in the tadpole of the frog. 



The question arises: Why do notches in the leaf never 



begin to grow while the leaf is attached to an intact 



plant, and why do they grow when the leaf is isolated? 



To this we are inclined to give an answer in the sense 



jf Bonnet, Sachs, 



deVries, and 



Goebel, namely 



that the flow of 



(specific ?) s u b - 



stances in the 



plant determines 



when and where 



dormant buds or 



anlagen shall be- 



FIG. 1 6. Growth of roots and shoots in a 



few notches of an isolated leaf 



of Bryophyllum calycinum 



gin to grow. Such 

 substances may 

 originate or may 

 be present in the leaf; but as long as it is connected 

 with a normal plant they will be carried by the cir- 

 culation to the growing points of the stem and of the 

 roots and they cannot reach the notches ; while when we 

 detach the leaf, either a new distribution or a new flow 

 of liquids will be established whereby the substances 

 reach some of the notches; and in these notches new 

 roots and a new shoot will be formed. When we 

 cut off a leaf and put it into moist air, not all but only 

 a few of the notches will, as a rule, grow out (Fig. 16); 



IX 



