18 REGENERATION 



their dry weight as well as that of the leaves was determined. 

 It was found that the dry weight of the leaves themselves (not 

 including the dry weight of the shoots and roots formed) was 

 considerably higher than was that of the sister leaves at the 

 beginning of the experiment. The increase in the dry weight of 

 the leaves was less, however, than the dry weight of shoots and 

 roots produced by the leaves. Three sets of experiments were 

 performed. In these three sets the leaves gained in dry weight 

 612 milligrams. The dry weight of shoots formed was 1.200 grams, 

 and the dry weight of roots formed was 352 milligrams. Hence 

 two and a half times as much material was utilized for the forma- 

 tion of new shoots and roots as for the growth of the leaf. Yet 

 it is of importance that not all of the material available in the leaf 

 for growth was used for regeneration. 



Table VI. — Duration of the Three Sets of Experiments, June 1 to 



30, 1920 

 I. Six pairs of sister leaves. 



a. Six leaves, fresh weight, 25.385 grams, dry weight, 



June 2 2 . 259 grams 



b. Six sister leaves, fresh weight, 24.120 grams, dry 



weight, June 30 2 . 404 grams 



Increase in dry weight of leaves in 6 145 milligrams 



Dry weight of shoots formed in b June 30 320 milligrams 



Dry weight of roots formed in b June 30 102 milligrams 



II. Seven pairs of sister leaves, 



a. Seven leaves, fresh weight, 28.490 grams, dry 



weight, June 2 2. 674 grams 



b. Seven sister leaves, fresh weight, 27.040 grams, dry 



weight, June 30 2 . 849 grams 



Increase in dry weight of leaves in 6 175 milligrams 



Dry weight of shoots formed in b June 30 383 milligrams 



Dry weight of roots formed in b June 30 92 milligrams 



III. Eight pairs of sister leaves. 



a. Eight leaves, fresh weight, 28.825 grams, dry 



weight, June 2 2. 552 grams 



b. Eight sister leaves, fresh weight, 28.500 grams, dry 



weight, June 30 2 . 844 grams 



Increase in dry weight of leaves in b 292 milligrams 



Dry weight of shoots formed in b June 30 497 milligrams 



Dry weight of roots formed in b June 30 158 milligrams 



This explains in part why in the normal plant no regeneration 

 of roots and shoots occurs in the leaf. In the normal plant all 

 material is used either for growth of the leaf or for growth of the 

 stem, apex, roots and stem itself, as will be seen later. 



