JACQUES LOEB 



357 



Proof That the Leaf Sends Nutritive Material Also in the Basal Direction 



of the Stem. 



When we suspend stems horizontally with one leaf at the apex, the 

 inhibitory effect of the leaf upon shoot formation is much stronger 

 when the apical leaf is on the upper side of the stem than when the 

 leaf is on the lower side of the stem. We can use experiments of the 

 latter type to show that the leaf sends nutritive substances to the 

 base as well as to the apex and that the fact that the leaf inhibits 

 shoot formation at the base is not due to the leaf failing to send nutri- 

 tive material in the direction of the base of the stem. The method of 

 proving this consists in measuring the influence of the mass of the 

 leaf upon shoot formation in the basal part of a horizontally suspended 

 stem. 



Stems were split longitudinally and suspended horizontally; each 

 stem having a leaf at the apex, and on the lower side of the stem.^ 

 Fig. 18 gives the result of such an experiment. Pieces of stems pos- 

 sessing two nodes and two leaves at the apical node are split longi- 

 tudinally, so that each half stem has one leaf at the apex and one bud 

 in the basal node. One leaf is left intact while the size of the sister 

 leaf is reduced considerably. In Fig. 18 Leaves I and la, II and 11a, 

 etc., are sister leaves. Practically each stem has produced a shoot at 

 the basal node, but the shoot is invariably greater in the stems in 

 the upper row where a whole leaf was at the apex than in the lower 

 row where the apical leaf was reduced in size. The drawing was made 

 on the 34th day of the experiment. It is obvious that the growth of 

 the basal shoots increases with the mass of the apical leaves and this 

 is proved by the relative weight of the leaves and shoots. 



Dtiration of Experiment, 39 Days. 



^ If the leaf is on the upper side, we get too much inhibition of shoot forma- 

 tion, whereby the experiment is rendered diiBcult. 



