394 SCIENCE PROGRESS 



the light previously, the change in curvature took place equally 

 in the light or in the dark. This is held to show that the 

 phototonus of the frond necessary for the geotropic reaction 

 can be obtained independently of the geotropic reaction itself. 

 An investigation of the reaction to stimuli of the hypocotyls 

 of young mistletoe seedlings has been made by Heinricher 

 (Ber. deut. bot. Ges. 34, 818-30, 191 6 ; Jahrb. f. wiss. Bot. 57, 

 321-62, 191 7), who finds that for three or four weeks after 

 germination the hypocotyls are negatively phototropic, and for 

 about two succeeding weeks negatively geotropic, but that the 

 latter does not become evident to any extent if the attachment 

 of the plant to the substratum takes place during the period 

 in which the hypocotyls are negatively phototropic. Van 

 Ameijden (Diss. Utrecht, 191 7 ; Versl. Verg. Kon. Akad. van 

 Wetensch. Amsterdam, 25, 1135-43, I 9 I 7)> working with oat 

 seedlings, shows that oxygen is necessary for the perception of 

 the geotropic and also of the phototropic stimulus. 



In a series of investigations on regeneration in Bryophyllum, 

 Loeb (Science, 44, 210, 1916 ; 46, 1 15-18, 191 7 ; Bot. Gaz. 63, 

 25-49, 191 7) has shown that on removal of all the leaves from 

 a stem except one apical one, the rate of geotropic curvature 

 when the stem is placed horizontally is comparatively rapid, 

 and is proportional to the mass of the leaf. If a single leaf is 

 left attached, but towards the base instead of at the apical 

 end, the curvature is less and is confined to the part of the 

 stem near the attached leaf. Root production runs parallel 

 with geotropic curvature. These results lead the author to 

 the conclusion that from each leaf root-producing substances 

 pass out towards the base of the stem, and shoot-forming 

 substances pass out towards the apex. The root-forming 

 substances produced in the leaf are absorbed in the stem and 

 bring about the growth of the cortical cells to which the geotro- 

 pic curvature is due. It seems likely that in Bryophyllum the 

 same substance (hormone) may control both geotropic curvature 

 and root production. 



In three papers read to the British Association for the 

 Advancement of Science in 191 5 and 1916 (British Ass. Rep., 

 85, 722, 1916 ; 86, 511, 1917) Miss Prankerd adduced evidence 

 in favour of the statolith theory of the organs of perception of 

 gravity. A statolith is defined as an organ free to move in the 

 cell containing it ; in many cases statoliths are starch grains. 



