THE INHIBITORY ACTION OF APICAL LEAVES 



103 



In Fig. 80, a is a piece of stem without leaf, b a piece of stem 

 with a reduced piece of leaf attached to the apex, and c a piece of 

 stem with a whole leaf attached to the apex. The right side of 

 the upper part of the stem opposite the leaf is cut off. The stems 

 of b and c have formed roots at the base on that side of the 

 stem where the leaf is, showing that the material for root 

 formation was carried in the descending current from the leaf. 

 Moreover, the mass of roots is greater in c than in b, corre- 

 sponding to the difference in the mass of the leaf. Later on, 

 however, roots may form in the whole circumference of the base 

 of the stem. Stem a, which had no leaf, has not formed any 

 roots at the base, but only the transitory air roots in nodes, 

 these air roots disappearing when the permanent roots at the base 

 are formed. No shoots were formed in b and c on the side of the 

 stem where the leaf is, showing the inhibitory effect of the 

 descending sap, but shoots were formed on the side opposite to 

 that of the leaf. The mass of shoots is greatest in c where the 

 mass of the leaf is greatest, is smaller in b where the leaf is reduced 

 in size, and smallest in a where there is no apical leaf. 



All these experiments were carried on simultaneously and lasted 

 from Dec. 7, 1922 to Jan. 5, 1923. 



The determinations of the dry weight show that the mass of 

 shoots produced per gram of dry weight of stem increases with the 

 size of the apical leaf, and that therefore the material of which the 

 shoots in b and c are formed is partly furnished by the descending 

 sap from the leaf (Table XXI). 



Table XXI 



Dry 



weight of 



stems, 



grams 



Dry 



weight of 

 shoots, 

 grams 



Dry 



weight of 

 basal 

 roots, 

 grams 



Weight of 



shoota 

 produced 



per 1 

 gram of 

 stem, 

 milli- 

 grams 



a. Six stems without leaves 



b. Four stems with reduced leaves. 



c. Five stems with whole leaves. . . 



21.5 

 31.0 

 46.0 



The dry weight of the mass of leaves in b was 0.470 gram, in c, 

 2.607 grams. 



