302 



QUANTITATIVE LAWS IN REGENERATION. I 



On the basis of these and of the writer's earlier 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, illumi- 

 nation, and aeration, approximately equal masses of roots and shoots, 

 regardless of the number of shoots or roots formed (except that a 

 moderate number of shoots may possibly permit a more complete 

 utiHzation 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 directly pro- 

 portional to the masses of the leaves. 



TABLE rv. 

 Duration of Experiment 33 Days. 



//. Ratio of the Mass of Shoots to the Mass of Roots Produced by 

 a Leaf Dipped in Water. 



When we dip a leaf with part of its edge into water, shoots and 

 roots form as a rule only in the wetted part of the leaf. It was of 

 importance to determine the ratio of dry weight of roots to the 

 dry weight of shoots produced in such cases. In the examples 

 already quoted this ratio was never less than one-third and never 

 more than one-half. The average taken from a large number of 

 experiments gave the ratio of the dry weight of roots to that of shoots 

 under such conditions as 0.42. This figure will be used in the 

 experiments of the next chapter. 



