JACQUES LOEB 713 



VII. General Remarks. 



As far as the polar character of root formation is concerned, the 

 experiments show that dormant buds for the development of air 

 roots exist in the axil of each leaf (apically from the resting shoot 

 buds) and that it is the rapid growth of the basal roots in the soil or in 

 water which prevents these roots from growing out in the normal 

 plant. 



To explain this inhibition it suffices to assume that a more rapidly- 

 growing organ in a plant generally inhibits the more slowly growing 

 organ of the same kind in other parts of the plant. This principle is, 

 perhaps, the most generally active in the phenomena of correlation. 

 The more abundant growth of the basal roots must find its explanation 

 on the assumption of the greater collection of water and solutes neces- 

 sary for root growth at the base of a normal or isolated piece of stem. 

 This follows from the fact proved in this paper that the mass of air 

 roots formed in an isolated piece of stem increases with the mass of 

 leaf attached to the stem and that the leaf has this influence only if 

 it is exposed to light. This indicates that the root formation is pri- 

 marily a phenomenon of nutrition and growth. 



Bayliss^ has called attention to a paper by Errera^ on "inhibitory 

 stimulation" in which this author discussed the influence of the apex 

 of fir trees on the direction of growth in secondary branches, and of the 

 apex of roots on the direction of growth of secondary roots. Errera 

 accepted Czapek's hypothesis of the formation of a specific antioxidase 

 as a consequence of the "geo tropic perception" and raised the ques- 

 tion whether the influence of the apex on the lower ramifications does 

 not consist essentially in sending to these branches, or in calling forth 

 in these branches the formation of, a substance antagonistic to this 

 antioxidase— a kind of antibody. This idea is, of course, very 

 hypothetical, and the writer without being aware of Errera' s sug- 

 gestion had offered a different explanation of the same phenomenon. '^ 



The assumption of the existence of specific inhibitory substances 

 which the writer had used tentatively in two preceding papers,^ and 



^Bayliss, W. M., Nature, 1918, cii, 285. 



9 Errera, L., Bull. Soc. Roy. hot. Belgique, 1904, xlii, 27. 



