JACQUES LOEB 705 



Halma's experiment the formation of shoots on the under side of a 

 piece of stem of citron when suspended horizontally was inhibited 

 by the more rapid growth of the shoots on the upper side of such a 

 piece of stem. 



The writer has already reported an experiment^' which proves 

 directly that the growth of a shoot on the upper side of a stem of 

 Bryophyllum, suspended horizontally, inhibits the growth of a 

 shoot on the lower side of such a stem. When we isolate a piece of 

 stem of Bryophyllum and remove all the leaves from such a piece 

 the two buds situated in the most apical node will grow out into 

 shoots. When we place a stem horizontally in such a way that 

 the line connecting the two apical shoot buds is vertical, both buds 

 will begin to grow out but the upper shoot will grow more rapidly 

 than the lower one and in the majority of cases the lower shoot will 

 soon stop growing, while the upper shoot continues to grow. When 

 we remove the upper bud, this inhibitory effect on the lower bud dis- 

 appears and the shoot on the lower side will grow out as vigorously 

 as the upper shoot would have done if its bud had not been removed. 



Our experiments show also that the path for the substances favor- 

 ing root formation is not identical with the path determining inhibi- 

 tion of shoot formation. Thus in Figs. 8 and 9 the inhibitory in- 

 fluences on shoot formation in the stem follow the conducting vessels 

 on the upper half of the horizontally suspended stem, while the root 

 formation is favored in the lower half of the stem. 



V. The Preformation of Root Buds in the Axil of a Leaf. 



We have seen that in the axil of each leaf of Bryophyllum calycinum 

 there is one bud capable of growing out into a shoot, though this 

 growth is inhibited in a healthy plant under normal conditions, and 

 the mechanism of this inhibition determines also the polar character 

 of regeneration as far as shoot formation is concerned. Roots can 

 develop anywhere on the stem and this causes the appearance as if 

 no preformation of root buds existed in the plant. Yet this appear- 

 ance is deceptive since as a matter of fact in the axil of each leaf there 

 is not only a preformed shoot bud but also a preformed root bud. 

 Curiously enough, this root bud lies a little above (apically from) 

 the shoot bud. Special experiments are required to demonstrate the 



