JACQUES LOEB 461 



in the dark had formed a single basal root though some had formed 

 tiny air roots (Fig. 8). The shoots formed in the dark had a small 

 mass and the typical etiolated shape. The most striking phenomenon 

 was the lack of root formation at the base of the stem in the dark. 

 The writer had already shown that the favorable influence of the leaf 

 on root formation in the stem also disappears when the leaf is deprived 

 of light." 



SUMMARY AND CONCLUSION. 



It is well known that a long defoliated piece of stem of Bryophyllum 

 calycinum forms shoots only at the apical or the two apical nodes, 

 while when such a stem is cut into as many pieces as there are nodes 

 each node produces shoots. It is shown in this paper that the dry 

 weight of shoots produced in the apical nodes of a long piece of stem 

 is approximately equal to the dry weight of shoots the same stem 

 would have produced if it had been cut into as many pieces as it 

 possesses nodes. Hence all the material which can be used for the 

 growth of shoots goes into the most apical part of the stem and this 

 accounts for the polar character of regeneration in this case.^ 



It seems that the mass of basal roots produced by a piece of de- 

 foliated stem also increases with the mass of the stem. 



^ A plant morphologist, to whom the writer showed these experiments, com- 

 mented that he was convinced that the shoot formation of an isolated piece of 

 stem was due to a "stimulus." If we accept this suggestion, it follows that the 

 "stimulus" for regeneration must have varied quantitatively with the mass of 

 the defoliated stem in our experiments, and this would lead us again to the idea 

 that the "stimulus" must be something material since it cannot well be spiritual. 



