GROWTH OF ROOTS AND SHOOTS IN THE LEAF 



39 



We have seen that the amount of shoot and root formation of a 

 leaf in the dark is only a small fraction of the quantity of regenera- 

 tion in the hght. It was next of interest to find out whether 

 there occurs also in the dark a diminution of the shoot formation 

 in the leaf when a piece of stem is attached to it, and whether 

 such an inhibition is accompanied in the dark also by a corre- 

 sponding increase in the dry weight of a stem. It was found that 

 the stems actually diminish or repress the already small amount 

 of shoot formation of a leaf in the dark and that the dry weight 



In dark 



Tig. 34. — The inhibitory effect of the stem occurs also in the dark, leaf a 

 producing a greater mass of shoots and roots than its sister leaf a\, which has 

 a piece of stem attached. Apr. 18 to May 9. 



of the stems increases to about the same amount in weight as the 

 shoot formation in the leaf is diminished. Figure 34 indicates 

 the difference in the appearance of the leaves with and without 

 stems attached when kept in the dark. The experiment lasted 

 20 days. The leaf a, without stem, produced more shoots than 

 its sister leaf ai with a half piece of stem attached. The stems 

 gained correspondingly in weight. The exact figures of the dry 

 weight measurements of the experiment are given in Table XIII. 



Table XIII 



Dry weight 



of leaves, 



grams 



Dry weight of Dry weight of 



shoots regen 



erated by 



leaves, 



grams 



roots regen- 

 erated by 

 leaves, 

 grams 



Set a. Nine leaves without stem . . . 



Set fli. Nine sister leaves with 



pieces of half stems attached 



0.007 

 0.004 



