THE VALIDITY OF THE MASS RELATION 53 



that individual buds may have been injured by parasites, etc. — • 

 the agreement of the figures seems remarkable. 



These results leave no doubt that within the limits of accuracy 

 of these experiments the dry weight of the shoots produced at the 

 apex of a long piece of defoliated stem is about equal the mass of 

 shoots the same stem would have produced had the buds in all 

 of its nodes been able to develop. 



4. Regeneration of Roots. — The regeneration of the basal roots 

 differs from the formation of apical shoots in this, that the apical 

 shoots begin to grow out almost immediately after the defoliated 

 piece of stem is isolated, while there is a long latent period before 

 the basal roots make their appearance. For this reason quanti- 

 tative measurements correlating the mass of the basal root forma- 

 tion with the mass of stem require probably a longer time than 

 that selected for our experiments. A glance at the drawings 

 will, however, convince the reader that the root formation com- 

 mences sooner in the stems with larger mass than in the stems 

 with smaller mass, regardless of the original position of the piece 

 of stem in the plant. Thus in Fig. 40 the large middle piece (3) 

 forms roots before either of the two more basal pieces, and Fig. 41 

 shows that the relative mass of roots produced seems also to run 

 parallel with the relative mass of the piece. The same phe- 

 nomenon is shown if we compare Fig. 37 with Fig. 38. It is. also 

 obvious in Fig. 39, so that we can say that the mass of roots pro- 

 duced by pieces of defoliated stem of Bryophyllum calycinum 

 increases under equal conditions with the mass of the stem. 



5. Influence of Light on Regeneration in a Defoliated Stem. — 

 To prove finally that we are dealing with the mass of material 

 produced by assimilation it is necessary to examine the effect of 

 light on regeneration in a defoliated stem. Eight such stems 

 were suspended in an aquarium kept dark by a double cover 

 of black cardboard, and eight equally long defoliated stems 

 were put at the same time into an aquarium exposed in the usual 

 way to daylight. The base of the stems dipped into water. All 

 conditions were alike except the illumination. After 23 days all 

 the stems exposed to light had formed large basal roots and large 

 shoots at the apex (right stem in Fig. 42). At the same time 

 none of the stems in the dark had formed a single basal root 

 though some had formed tiny air roots (left stem in Fig. 42). 

 The shoots formed in the dark had a small mass and the typical 

 etiolated shape. The most striking phenomenon was the lack 



