Scientific Proceedings (87). 



two main colloids are unequally distributed in the two phases of 

 the system. True adsorption must as Zsigmondy has pointed out 1 

 play an important part but the reactions imply that absorption 

 also takes place. The arrangement of the denser continuous 

 phase of the gel in the form of a fine sponge or of a close mesh of 

 plates or fibers would offer conditions in which both adsorption 

 and absorption might occur. The parallelism of hydration in 

 biocolloids with hydration and growth in plants with regard to 

 temperature implies identity of structural arrangement and simi- 

 larity of action. The end points, maxima or totals in the swell- 

 ing of the biocolloids given above probably represent the point at 

 which dispersion assumes a high rate, and available information 

 is not sufficient to identify this with the upper temperature limit 

 of growth. 



137 (1315) 



The chemical basis of morphological polarity in regeneration 

 By Jacques Loeb. 



[From the Rockefeller Institute for Medical Research.} 



When a piece is cut out of the stem of a plant (Bryophyllum 

 calycinum) the most apical buds will grow out into shoots, while 

 roots develop chiefly but not exclusively at the basal end. The 

 writer suggests the following explanation of this phenomenon of 

 polarity. In the normal stem the growing region at the apex as 

 well as the leaves send out special inhibitory substances toward 

 the base of the plant which prevent the growth of the more basally 

 situated dormant buds capable of giving rise to shoots. When a 

 piece is cut out from the stem these inhibitory substances con- 

 tinue to flow in the piece toward the base and the most apical 

 node will be the first one sufficiently free from these inhibitory 

 substances and hence the two dormant buds situated at this node 

 will grow out first. As soon as they grow out they produce and 

 also send out inhibitory substances toward the base, thereby pre- 

 venting the more basally situated buds from growing out into 

 shoots. 



A brief outline of the experiments supporting this hypothesis 

 has been published in Science. 2 



1 Chemistry of Colloids, p. 59, 191 7. 

 s Loeb, J., Science, 1917, xlvi, 547. 



