CHEMICAL AND PHYSICAL CHANGES DURING 



GEOTROPIC RESPONSE 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 262 



Thomas G. Phillips 



Introduction 



The work reported in this paper was undertaken with the object 

 of making as complete a study as possible of all the chemical and 

 physical processes that might be involved in geotropic response. 

 It was hoped in this way not only to add something to the knowl- 

 edge of the mechanics of geotropic bending, but also to find some 

 quantitative differences which are associated with the differing 

 rates of growth of the two flanks of the responding organ. It 

 became necessary to drop the work before it was complete. Such 

 results as were obtained are reported in the hope that they may 

 prove of some value to others interested in the problem. 



Several studies of one or more of the factors which might be 

 involved have been made. Kraus (8) found that the water content 

 of the convex flank of organs stimulated geotropically is greater 

 even before bending begins. He also made determinations of 

 reducing sugars and titration acidity on the juice expressed from 

 the organs. He concluded that when a stem capable of negative 

 geotropic response is laid horizontally, increased sugar formation 

 begins at once, and the amount of free acid decreases. This occurs 

 especially on the lower side. There is a movement of water from 

 the upper to the lower side. Thus the concentration of sugar in the 

 juice of the lower side becomes less than in that of the upper. 



Miss Schley (9), working with shoots of etiolated Vicia Faba 

 seedlings, found rather complex changes in the titration acidity 

 after exposure to gravity. First the concave side was more acid, 

 then the convex, then they became about equal while bending was in 

 progress. After the tip had passed the vertical, the concave side 

 became the more acid, but this difference gradually disappeared. 

 She found the water content somewhat greater on the convex side, 



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