no INFLUENCE OF THE EXTERNAL CONDITIONS ON GROWTH 



sufficiently considered. At the same time the main stems of Gymnosperms become 

 hypotrophic, and those of the oak epitrophic. when placed horizontally, just as 

 in the case of the lateral branches of these plants, and of Fagus and Tilia. 

 Finally, if grass-haulms are laid horizontally and their growth in length mechanically 

 restrained, the under sides of the nodes, which would become convex if geotropic 

 curvature were allowed, become instead distinctly thicker on this side \ 



It appears that the inversion of a shoot frequently somewhat retards 

 its growth in length, and that this is slightly accelerated when it is returned 

 to its normal position. 



Thus Vochting 2 found that the drooping branches of the weeping willow grew 

 more slowly than the erect ones, and according to Raciborski 8 the stem-apices 

 of certain tropical climbers undergo a retardation of growth if they fail to come 

 into contact with a support, and therefore hang downwards, and they may even 

 ultimately die. A retardation of growth was also observed by J. Richter 4 in 

 inverted shoots of Chara, and by Elfving 8 in the inverted sporangiophore of 

 Phycomyces nitens. In the last case microscopical measurements were made at 

 short intervals of time alternately in the inverted and normal position, and during 

 each period of inversion the same retardation was shown. A similar action has 

 been observed by J. Ray 6 in the case of Sterigmatocystis alba. 



In their normal position,however,the growth of stems androots would not 

 appear to be perceptibly affected by considerable increases of gravitational 

 force. At least Elfving (1. c.) and Fr. Schwarz 7 observed the same rate 

 of growth in control plants, and in those subjected to centrifugal forces of 

 from 30 to 50 g. Still higher forces would, however, undoubtedly produce 

 some effect, even if merely by the increased pressures and tensions they 

 create 8 . Mottier 9 , however, observed that the rate of growth remained 

 normal in maize roots after being subjected for 24 hours to a centrifugal 

 force of l,8oo g. Elfving and Schwarz also found that no change in the 

 rate of growth took place in seedlings or in the sporangiophore of Phycomyces 

 when rotated horizontally on a klinostat, so that geotropic curvature was 

 avoided, but the force of gravity directed perpendicularly to the long 

 axis of the growing organ. Under such circumstances, however, growth is 



1 Pfeffer, Druck- u. Arbeitsleistungen, 1893, p. 396, and the literature there given. 



2 Vochting, Bot. Ztg., 1880, p. 599; Organbildung, 1884, p. 78; Sorauer, Forsch. a. d. Geb. 

 d. Agric., 1885, Bd. viil, p. 235. Vochting (Bewegung d. Bliithen, 1882, p. 122) found that the 

 inverted peduncles of certain flowers become shorter and thicker than when grown in the normal 

 position. 



Raciborski, Flora, 1900, p. 35. Correlative influences require consideration in all such cases. 



Richter, Flora, 1894, p. 402. 



Elfving, Beitrag z. Kennt. d. Einwirkung der Schwerkraft auf Pflanzen, 1880 (repr. from Act. 



Soc. 



Sci. Fennic., Bd. XII). The experiments are not altogether satisfactory. 



Ray, Rev. ge"n. d. Bot., 1897, T. ix, p. 255. 

 Schwarz, Unters. a. d. Bot. Inst. in Tiibingen, 1881, Bd. I, p. 53. 



[These could be practically eliminated by using aquatic plants or seedlings immersed in well- 

 aerated nutrient solutions in closed tubes.] 



9 Mottier, Annals of Botany, 1899, Vol. xin, p. 355. 



