JACQUES LOEB 



339 



The elements capable of giving rise to roots are not confined to the 

 nodes but exist all over the stem in a definite layer of the cortex. It 

 can be shown that the sap from the leaf flowing towards the base of a 

 stem favors the growth of roots and inhibits the growth of shoots. 



Experiments on Potted Plants. 



When we cut off the top of a potted plant of Bryophyllum calycinum, 

 leaving a stem containing only two leaves at the apical node, none 



Fig. 2. Top of plant removed; two leaves at apex which prevent growth of 

 all the buds below. 



of the buds on the stem below the two leaves will grow out (Fig. 2), 

 so long as the leaves are alive and able to send their sap to the base 

 of the plant. The buds situated in the axil of the two leaves may 

 after some time grow out. The two leaves inhibit therefore the 

 growth of all the buds situated more basally (Fig. 2). Each leaf 

 inhibits the growth of the buds situated in the same half of the stem, 

 and in order to prove this we remove in a second set of experiments 



