JACQUES LOEB - 359 



Other experiments gave similar results. While the experiment 

 does not reveal any strict proportionality between mass of leaf and 

 mass of basal shoot produced, the increase of the mass of shoots with 

 the mass of the leaves is unmistakable. 



We therefore come to the following conclusion. The leaf sends 

 material for growth in both directions of the stem, to the apex as 

 well as to the base. It also behaves as if it sent out inhibitory sub- 

 stances in both directions, but if this be the case there must exist a 

 considerable difference in regard to the mass of the latter. While 

 much or almost all of the inhibitory substance is sent in basal direc- 

 tion, only traces of it are sent in an apical direction, so that special 

 experiments are required to demonstrate the inhibitory effect in the 

 apical parts of the stem. 



A glance at Fig. 18 confirms also the statement that the mass of 

 roots formed in the basal part of a stem increases with the mass of 

 the apical leaf. The stems in the upper row with a whole leaf at the 

 apex have a greater mass of shoots and roots than the stems in the 

 lower row with a reduced leaf. 



DISCUSSION. 



We have shown in this paper that a leaf inhibits the regeneration 

 of shoots in the basal parts of the stem and that this inhibition is di- 

 minished or ceases when the mass of the leaf is reduced below a cer- 

 tain limit. If the inhibitory influence of the leaf is due to inhibitory 

 substances sent out by the leaf to the basal parts of the stem we 

 must conclude that traces of these inhibitory substances flow also to 

 the apex of the leaf since it is possible to demonstrate slight inhibitory 

 influences of the leaf in the buds situated apically. 



The influence of the leaf upon the regeneration of roots is exactly 

 the reverse from that on the regeneration of shoots. The leaf favors 

 the formation of roots in the basal parts of the stem and this favor- 

 able influence upon regeneration of roots in the basal part of a stem 

 increases with the mass of the apical leaf. 



This gives us an indication of the role which a leaf plays in the 

 establishment of the polar character of regeneration in the stem of 

 Bryophyllum calycinum. When a piece of stem is cut out with a leaf in 

 the middle, the leaf sends out nutritive material in both directions of 



