32 



REGENERATION 



a piece of stem. At the end of the experiment, the dry weights of 

 the leaves, shoots, roots, a and ai, and of the shoots and roots 

 produced by them, and of the half stems 61, which had been left 

 in connection with the leaves, were determined. It was found 

 that the dry weight of the half stems 61 (Fig. 30), left in connec- 

 tion with the leaves a\, had increased and that this increase in 

 weight was sufficient to account for the excess in the dry weight 

 of roots and shoots formed in the leaves a, without pieces of stem. 

 In other words, the inhibitory action of the stem on the regenera- 

 tion in the leaf was due to the fact that the leaf sent part of its 



Fig. 30.^ — ^Leaf ai, with a small piece of stem attached, produces a smaller 

 mass of shoots and roots than the sister leaf a without stem. The piece of 

 stem increases in mass, especially through callus formation, and this accounts 

 for the inhibiting action of the stem on shoot and root formation in leaf. Axillary- 

 bud of stem removed. Apr. 6 to 26. 



material into the stem, which otherwise would have been avail- 

 able for regeneration in the leaf. 



In such experiments the axillary bud of the half stem left in 

 connection with the leaf often grows out and it is natural to 

 infer that this growth withdraws material from the stem. It 

 can be shown, however, that the stem inhibits the regenerative 

 growth in the leaf also if this axillary bud is removed at the 

 beginning of the experiment; and that, in this case also, the inhibi- 

 tory influence of the piece of half stem on regeneration is due to 

 the fact that the leaf sends part of the material produced by 

 assimilation into the stem. In the stem it is used chiefly for 



