84 REGENERATION OF BRYOPHYLLUM CALYCINUM 



the half stems intact, while the sister leaf at the base of the other half 

 stem is reduced in size, it is possible to find out whether the mass of 

 the shoots regenerated at the apex of each half stem bears any rela- 

 tion to the mass of the two leaves. Such experiments were made by us 

 and as a rule six or more different stems were used in one experiment.^ 

 Many experiments are lost for the reason that the leaf at the base of 

 a stem wilts or perishes much more rapidly than a leaf entirely de- 

 tached from a stem; the latter may last for months while the former will 

 usually wilt after a few weeks. For this reason it is more difficult to 

 obtain exact results in investigating the influence of the mass of the 

 leaf on the mass of the shoots formed at the apex of a stem than in 

 investigating this influence upon the mass of shoots regenerated by 

 isolated leaves. But in watching the condition of the leaves and real- 

 izing that we can only utilize an experiment when all the leaves 

 remain intact we are able to obtain reliable results. This source of 

 error due to wilting and decay of the leaf attached to the base of a 

 stem which restricts the duration of the experiments is greater when 

 the thin summer leaves are used than when the more fleshy and 

 more durable winter leaves are utihzed. 



We shall first give the numerical results of some experiments in which 

 only the fresh weight of the leaves and of the shoots regenerated by 

 the stem was ascertained (Table I). 



In Experiment 3 of Table I, the leaves of both half stems were left 

 intact; 1 gm. of leaf in one set caused the production of 213 mg. of 

 shoots in the stem, while 1 gm. of leaf of the other set produced 240 

 mg. of shoots in the apex of the stem. This shows the degree of accu- 

 racy to be expected in these experiments. 



In the three other experiments the masses of the two sets of sister 

 leaves varied considerably. Thus in Experiment 1 the masses of the 

 leaves were approximately in the ratio of 1 : 6 (2.8 : 19.0) ; the masses 

 of shoots produced by the two sets of stems were also approximately 

 in the ratio of 1 : 6, namely 0.44 : 2.8. Experiment 2 gave similarly 

 good results. The ratio of the two masses of sister leaves was approx- 

 imately 1:5, namely 3.5 : 18.5, and the masses of shoots produced 

 by the stem were also approximately in the ratio of 1 : 5, namely 

 0.7 :3.6. 



2 Loeb, Proc. Nat. Acad. Sc, 1918, iv, 117. 



