38 



REGENERATION 



The material produced in a pair of sister leaves depends on their 

 relative size. On the other hand, a piece of stem of a given size 

 can in a given time consume only a limited quantity of material. 

 Hence when a small piece of stem with 2 sister leaves is split 

 longitudinally and the size of 1 leaf is reduced, the inhibitory 

 effect of the piece of stem on regeneration in the leaf will be more 

 complete in the reduced than in the whole leaf. Figure 32 

 shows that this is the case. On the other hand, when the piece 

 of stem is very small, its inhibiting power on regeneration in the 

 leaf approaches zero. This is illustrated in Fig. 33, where one 



Fig. 33. — Sister leaves. The larger piece of stem inhibits the formation of 

 shoots and roots in the leaf more completely than the smaller piece of stem. 



leaf is connected with a piece of stem about 25 millimeters long, 

 while the sister leaf had only a piece of stem about 4 millimeters 

 long. The inhibitory effect of this small piece of stem was very 

 slight compared with the inhibitory effect of the larger piece. 

 When the piece of stem is sufficiently large the inhibitory effect 

 on regeneration in the leaf may become complete. 



In most of the experiments referred to in this chapter the apex 

 of the leaf dipped into water. This is, however, not a necessary 

 prerequisite; what has been said above about the inhibitory effect 

 of a piece of stem on the shoot and root formation in a leaf 

 remains true also when the leaves are suspended entirely in 

 moist air, as shown in Fig. 28. 



