714 PHYSIOLOGICAL BASIS OF POLARITY. II 



which was based on the experiments of geneticists, is not needed for 

 the explanation of the results published in this paper. 



In the next paper the writer intends to furnish direct proof for the 

 fact that the isolation of a piece of a plant leads to a change in the 

 flow and distribution of sap and that this change in the distribution 

 determines the starting of growth of formerly dormant buds which 

 is the essential feature in regeneration. 



SUMMARY 



1. The experiments show that the mass of air roots formed in a 

 stem increases with the mass of the leaf attached to the stem, though 

 it has not been possible to establish an exact mathematical relation 

 between the two masses, owing to unavoidable sources of error. 



2. Darkened leaves do not increase the mass of roots formed. 



3. In stems suspended horizontally air roots appear on the lower 

 side of the stem, with the exception of the cut end where they usually 

 appear around the whole circumference of the stem. When the lower 

 half of a stem suspended horizontally is cut off, roots are formed on 

 the upper side. It is shown by experiments on leaves suspended 

 horizontally that the more rapidly growing roots and shoots on the 

 lower side inhibit the root and shoot formation in the upper half of 

 such a leaf; and likewise the more rapid formation of roots on the 

 lower side of a horizontally suspended stem seems to account for the 

 inhibition of root formation on the upper side of such a stem. Like- 

 wise the more rapid growth of shoots on the upper side of a stem sus- 

 pended horizontally is likely to inhibit the growth of shoots on the 

 lower side. 



4. Each leaf contains in its axil a preformed bud capable of giving 

 rise to a root, which never grows out in the normal stem on account 

 of the inhibitory influence of the normal roots at the base of the 

 plant. These dormant root buds are situated above (apically from) 

 the dormant shoot bud. The apical root buds can be caused to 

 develop into air roots when a piece of stem is cut out from a plant 

 from which the leaves except those in the basal node of the piece are 

 removed. The larger these basal leaves the better the experiments 

 succeed. 



