14 ANNALES DE L'INSTITUT PASTEUR 



I)U(ls in tlie siem, second, the callus formation at the basai end 

 of llio stem, and, third, Ihe geotropic ciirvaturc of the stem, 

 ail Ihree of AvhicJi may be observed in the same pièce of stem 

 atlachod to a leaf, as is the case in Fig. 1 . When we eut a 

 pièce of stem with onc leaf attached to it (as in Fig. 1) from a 

 plant, such a stem will form a shoot from its free bud (in the 

 axil of the leaf which was removed), and the mass of this shoot 

 may equal or even slightly exceed the mass of shoots produced 

 by the sister leaf which is not attached to a stem (as in Fig. 2). 

 We can easily nndeistand that the same material may be 

 utili/ed for shool production in the leaf and in the stem. But 

 in addition such a stem produces a mass of callus at its basai 

 end, Ihe material for which also comes from the leaf. And 

 finally, a third form of growth takes place in the stem at the 

 expense of material from the leaf and this results in geotropic 

 curvature. 



The connection between geotropic curvature of a stem and 

 the mass of the leaf connected with it can be demonstrated and 

 sincethis relation is a récent discovery (as far as the writer is 

 aware) it may be brielïy discussed. The writer found a year 

 ago that, if a pièce of stem is eut out from Bryophyllum and 

 suspended horizontally in moist air, the stem will gradually 

 bend until it finally assumes the shape of a U with the concave 

 side above (Fig. 3). It was found that this geotropic cuiva- 

 ture is due to a longitudinal growth of a certain layer of cells 

 in the cortex on the lower side of a horizontally placed stem ; 

 as a conséquence of this growth the whole stem bends in the 

 way described. 



Now if our assumption is true that the inhibiting effect of 

 the stem is due to the absorption of that material from the leaf 

 which would bave served for régénération in the leaf ; and that 

 this material is utilized for the growth of certain cells in the 

 stem, we should be able to show that the geotropic curvature 

 increases with the mass of the leaf attached to the apical end 

 of the stem. Our experiments show in a striking way that 

 this is correct. 



Stems, each of which having a leaf at the apical end were 

 suspended horizontally in moist air; the leaves and stems 

 were approximately equal in size. The leaves of one set were 



