JACQUES LOEB 303 



///. The Inhibitory Influence of the Stem on Shoot Production in 

 the Leaf of Bryophyllum calycinum. 



Only the leaf isolated from the stem is capable of forming shoots; 

 it suf&ces as a rule to leave a piece of stem connected with the leaf to 

 cause retardation or inhibition of the growth of the dormant buds in 

 the notches of a leaf.^ There are two possible reasons for the in- 

 hibitory action of the stem on the shoot and root formation in the 

 leaf. The material available for root and shoot formation in the leaf 

 either flows naturally into the stem and hence the buds in the notches 

 of the leaf cannot grow out on account of lack of material for growth;^ 

 or second, the stem sends into the leaf a substance preventing the 

 growth of the notches in spite of the fact that the material needed 

 for the growth of the dormant buds in the notches of the leaf is 

 available. 



Only quantitative experiments allow us to decide between the two 

 possibilities. If the assumption is correct that the leaf normally 

 sends the material which can be utilized for the growth of shoots 

 and roots into the stem, the stem in connection with a leaf should 

 gain in weight and this gain should be equal to the mass of shoots 

 and roots the same leaf would produce when separated from the stem. 

 If the other possibility is correct, and if we are dealing with the 

 effect of inhibitory substances sent into the leaf, no such increase in 

 the dry weight of the stem need occur. My experiments give a clear 

 answer in favor of the first possibility; namely, that the inhibitory 

 effect of the stem upon the shoot and root production in the leaf is 

 due to the fact that the material in the leaf which could be utilized 

 for shoot and root formation flows normally into the stem, as long 

 as the leaf is connected with the stem and the sap flow is not inter- 

 rupted; while when the leaf is separated this material becomes 

 available for the growth of shoots and roots in the leaf, and the 

 inhibition ceases. Of course, we cannot determine directly which 

 mass of shoots and roots the inhibited leaf would have produced if 



" This inhibition cannot be permanent since before the falling off of the leaf 

 the sap flow between leaf and stem will cease and this will have the same effect 

 as the cutting off of the leaf. 



■^ Loeb, J., Ann. Inst. Pasteur, 1918, xxxii, 1. 



