130 



REGENERATION 



which is not far from what we should expect according to the 

 mass law. 



If we inquire how it happens that at first the apical leaf, if it 

 is sufficiently large, inhibits even transitorily the shoot formation 

 on the side of the stem opposite to that of the leaf, we can only 

 suggest that it might be connected with a growth of tissues in 

 the stem. Should the inhibition be correlated with the fact that 

 the growth giving rise to geotropic curvature of the stem precedes 

 that of the regenerative processes? The reader will notice that 

 this curvature increases with the mass of the apical leaf and that 



Fig. 106. — Same stems as in Fig. 105, 5 clays later, May 29. In stem hi, 

 with whole leaf, a shoot on the upper side has grown rapidly, being larger than 

 the shoots in stem a\. 



the difference in curvature is more marked at first than later. It 

 is not impossible that this growth in the stem niight cause indi- 

 rectly an inhibition of shoot formation. The main fact is that 

 these inhibitory effects of the second order exist only at the 

 beginning. 



If we try to explain all of these phenomena of inhibition of the 

 first and second order in harmony with the theory of the polar 

 character of regeneration at which we arrived, we must assume 

 that the growth of the stem caused by the descending sap from 

 a leaf leads to a retardation or complete inhibition of the growth 

 of shoots in the basal part of the stem. In the direct path this 

 inhibition is most complete (inhibition of the first order). Out- 

 side the path the inhibition is less but still noticeable in the form 



