iQ2o] PHILLIPS— GEOTROPISM 169 



but the samples were taken after bending was practically complete. 

 The percentage of sugar in the convex flank was considerably- 

 lower than in the concave, after an exposure of 45 minutes. 



In various roots exposed to gravity Czapek (3) found an 

 accumulation of intermediate products of oxidation of certain 

 amino acids, due to the presence of an antienzyme which inhibits 

 the normal oxidation of these substances. He found no differences 

 between the upper and lower flanks in this respect. Grottiax (7) 

 and Grafe and Linsbauer (5) were unable to confirm Czapek's 

 results. The latter workers (6) found that geotropic response 

 causes no differences in catalase activity. 



Small (10) found increased permeability in the cortical cells of 

 both sides of root tips of Vicia Faba when exposed to gravity. 

 The permeability of the lower sides showed a greater increase 

 than that of the upper side. 



Changes in the viscosity of the protoplasm during geotropic 

 stimulation were studied by Weber (ii), who found that the 

 viscosity is lessened. Zollihofer (12) was unable to confirm 

 this result, and states that the method used is subject to large experi- 



mental errors. 



Experimental work 



The first material used in this work was nodes of corn that had 

 completed their growth. The node was cut out, together with 

 about half the internodes above and below, and the sheath removed. 

 The node was then planted horizontally in a bank of moist sand in 

 a box from which light w r as excluded. This material is especially 

 good because no growth occurs aside from that due to the action 

 of gravity, and because the region which bends in most cases is 

 very clearly defined. After exposure to gravity this region was cut 

 out and divided into upper and lower flanks. There are at least 

 two objections to the use of corn nodes. First, suitable material 

 can be obtained only during a comparatively short time each year. 

 Second, whether a given node will respond to gravity. is very un- 

 certain. Some nodes that apparently were healthy and in good 

 condition did not respond at all, and others which showed no evi- 

 dent differences responded readily. This makes practically impos- 

 sible a study of the period before visible bending begins. 



