On a method of studying Geotropism. 
BY 
ANNA BATESON, 
Newnham College , Cambridge , 
AND 
FRANCIS DARWIN, F.R.S., 
University Lecturer in Botany , Cambridge. 
I T is commonly assumed, in accordance with the teachings 
of Sachs, that the gravitation-stimulus which produces 
geotropic curvatures acts most strongly when the geotropic 
organ is placed horizontally. In other words, when an organ 
is placed obliquely, it is in a less favourable position for 
the development of geotropism than when it is horizontal 1 . 
On the other hand, Elfving 2 has given evidence to show 
that in the case of roots the position of maximum effect is 
when the apex of the root is directed vertically upwards, 
i.e. when the organ is at i8o° from its normal position. 
Our inquiry on this question is far from complete, and is 
published rather as pointing out a new method of attacking 
the problem, than as by any means solving it. 
The subject is one on which it is difficult to obtain satis- 
factory evidence. Thus, if we compare two negatively 
geotropic organs placed obliquely, so that the free end of 
one of them is above, while that of the other is below the 
horizon, we are at once confronted with a well-known diffi- 
culty. Assuming that the horizontal is the position of 
maximum effect, we must suppose that the stem which is 
beneath the horizon, and which therefore approaches the 
1 See Sachs, Arbeiten, ii. p. 240, i. p. 454. Flora, 1873, p. 326. 
2 Acta Soc. Scient. Fennica, 1880. The question is discussed by Vines in his 
Phys. of Plants, p. 460. 
[Annals of Botany, Vol. II. No. V, June 1888.] 
F 
