JACQUES LOEB 653 



experiment, and &i the mass at the end, we should expect to find that 



_ (^ = 



bi — h > a — ai or that ; 7 < 1. Table I shows that this 



ai -\- bi — b 



is correct. The average ratio of is 0.87. 



ai -\- bi — b 



When a leaf is connected with a stem which prevents regeneration 

 in a leaf the inhibitory effect is therefore due to the fact that the 

 material available for the regenerative growth in the notches of the 

 leaf flows into the stem. In fact 14 per cent more dry weight goes 

 from the leaf into the stem than would go into the growth of the 

 regenerating leaf. For some reason the flow of sap into the regenerat- 

 ing parts in the notches of a leaf seems to be less complete than the 

 flow of available material into the stem. 



II. 



The material which goes into the stem is used for different purposes; 

 it may cause the growth of an axillary shoot in the stem as in Fig. 1 . 

 Part of it causes an increase in the mass of the stem. The stippled 

 lines in Fig. 1 indicate part of the increase in the mass of the stem. 

 This increase is greatest at the basal end where it constitutes the callus. 



In a paper previously published^ the writer has called attention to 

 the fact that when a piece of stem is left in connection with a leaf 

 the inhibitory effect on the formation of roots in the leaf increases 

 with the size of the piece of the stem but less rapidly than this. This 

 is due to the fact that the increase in mass of the stem is not the same 

 throughout the whole length of the stem but that it is greater at the 

 base and possibly also (though to a lesser degree) in the region of 

 a node. 



Hence the increase in mass of a stem consists of the sum of two 

 quantities, c -\- I Ci, where c expresses the mass of the callus which 

 does not necessarily increase with the mass of the stem, and I Ci, 

 where / is the length of the stem and Ci the increase in the mass per 

 cm. length of a stem with unit periphery. It is obvious why the 

 inhibitory power of a stem increases generally with its length but 

 less rapidly. 



^Loeb, J., Ann. Inst. Pasteur, 1918, xxxii, 1. 



