16 



REGENERATION 



furnished by the leaf can be utiHzed more fully than when all of 

 the material goes into one shoot. This is indicated in the figures 

 of Table IV. 



On the basis of these and numerous similar experiments we can 

 enunciate the following law: 



Equal masses of sister leaves of Bryophyllum calycinum produce, 

 in equal time, under equal conditions of temperature, moisture, 

 illumination, and aeration, approximately equal masses of roots 

 and shoots, regardless of the number of shoots or roots formed 

 (except that a comparatively larger number of shoots may 

 possibly permit a more complete utilization of the material 

 furnished by the leaf than if only one shoot is formed). When 

 the masses of two sister leaves are unequal, the masses of shoots 

 and roots produced by them are, within the limits of the accuracy 

 of the experiment, directly proportional to the masses of the leaves. 



To complete the proof that we are dealing here with the action 

 of the quantity of material produced by assimilation it remains to 

 be shown that the results described occur only in the presence of 

 light, while in the dark the production of roots or shoots in an 

 isolated leaf of Bryophyllum is negligible. The slight regeneration 

 in the dark occurs at the expense of material which was contained 

 in the sap at the time the leaf was placed in the dark. 



Twelve pairs of sister leaves were used, all of which were sus- 

 pended so that their apices dipped into water as in Fig. 18. 

 One leaf (aj) of each pair was exposed to scattered dayhght, while 

 the 12 sister leaves (a) were kept in the dark, but all at the same 

 temperature. The experiment lasted from Mar. 13 to Apr. 4. 

 The total mass of shoots and roots produced in the dark was less 

 than 14 per cent of that produced in the fight during the same 

 time (Fig. 18 and Table V). 



