52 SCIENCE PROGRESS 



At the same time the hypocotyls lose their geotropic irritabiUty, 

 although they are still able to respond to changes in light and 

 are still able to elongate. On replacement in the light the 

 statolith starch grains are re-formed after one and a half to 

 two days, and at the same time the organ regains its ability to 

 respond to gravity. 



Investigations have been made by a few workers with a 

 view to determining whether geotropic curvatures can be 

 correlated with other changes in the curving organ. Thus A. 

 Trondle (" Uber die ersten Stadien der geotropischen Kriim- 

 mung," Vierteljahrssch. der Naturf. Ges. in Zurich, 62, Z7'^~?)77i 

 191 7) treated seedling roots of Lupinus albits with a 2N to 4N 

 solution of sodium chloride after the roots had exhibited a 

 geotropic curvature. This treatment brought about a lessening 

 of the curvature, and the curvature was completely removed if 

 the radius of curvature was greater than 14 millimetres. On 

 the contrary, if the curved roots were treated with boiling water 

 instead of the strong salt solution, the curvature remained. 

 Treatment of unstimulated roots with the strong salt solution 

 and with boiling water produced in each case a shortening of 

 the root, but in the case of the former the reduction in length 

 was about three times as great as in the latter. Trondle 

 concludes from these results that in the first stage of geotropic 

 stimulation there results a difference in the elasticity of the cell 

 walls on the two sides (upper and lower) of the root, so that if 

 the turgor of the cells remains the same a curvature must 

 result. 



T. G. Phillips (" Chemical and Physical Changes during 

 Geotropic Response," Bot. Gaz., 69, 168-178, 1920) examined 

 the upper and lower sides of Vicia and Zea undergoing geotropic 

 curvature with regard to differences in composition of 

 the two sides. Water content, acidity as determined by 

 titration, distribution of sugars and nitrogen compounds, and 

 katalase activity were determined, but the author concludes 

 that the curvature cannot be correlated with any of these. 

 On the other hand E. O. Schley (Bot. Gaz., 70, 68-91, 1920), 

 in a similar investigation, found there was a change of poly- 

 saccharides into sugars on the convex side, while a temporary 

 increase of osmotic concentration on this side was also found. 

 The respiration in a curving shoot is also greater on the convex 

 side. The author concludes there is a definite sequence of 

 changes in a shoot subjected to geotropic stimulation, these 

 being (a) increase in respiration, (b) increase in acidity, (c) in- 

 crease in turgor, (d) increase in hydrolysis of polysaccharides 

 on the convex side. 



A curious case of reaction to the gravitational stimulus has 

 been recorded by H. Coupin ("• Sur une tige a geotropisme 



