40 



REGENERATION 



The 9 leaves (a) without stems formed in all 77 milligrams of 

 shoots and roots, while the sister leaves (oi) with a piece of half 

 stem attached, formed in all 10 milligrams of shoots and roots, a 

 difference of 67 milligrams. The half stems had at the beginning 

 a dry weight of 0.454 gram, while the half stems of ai had at the 

 end of the experiment a dry weight of 0.505 gram, an increase of 

 51 milHgrams. Hence the half stems in Set Ui gained in the dark 

 about enough in dry weight to account for the inhibitory effect 

 of the stem of the leaf cii on regeneration in the leaf. In this 

 experiment the stems formed no axillary shoot. In a repetition 

 of the same experiment in the dark, in which 17 pairs of leaves 

 with half stems were used, 7 of these leaves in which the stems 

 remained attached formed axillary buds. As a consequence 

 more material flowed from the leaves into the stems and the 

 inhibition of shoot and root formation in the leaves with half 

 stems attached became even more complete. Table XIV gives 

 the results. The experiment lasted 22 days. 



Table XIV. — Dark Experiment 



Dry weight 



of leaves, 



grams 



Dry weight of 

 shoots regen- 

 erated by 

 leaves, 

 grams 



Dry weight of 

 roots regen- 

 erated by 

 leaves, 

 grams 



Set a. Seventeen leaves without 

 stems 



Set b. Seventeen sister leaves with 

 pieces of half stems attached 



1.740 

 1.732 



0.161 



0.005 



0.019 



The leaves without half stems produced in all 175 miUigrams 

 more dry weight of shoots and roots than the leaves with half 

 stems attached, in which the inhibition of root and shoot forma- 

 tion was almost complete. The dry weight of 17 half stems at 

 the beginning was 0.571 gram, at the end 0.879 gram. This 

 latter figure included the weight of 7 axillary shoots. Hence the 

 dry weight of the stems increased by 308 milligrams, more than 

 enough to account for the inhibitory action of the stems on shoot 

 and root production in the leaves with half stems attached. 



In these experiments the material sent l)y the leaf into the stem 

 in the absence of light had been formed previously by the light. 

 The regeneration of plants in the dark resembles the regeneration 



