572 Darwin . — On Geotropism and the 
some io°-20° from the vertical, the curvature is in the right 
direction. Figs. 3 and 4 show that the cotyledon has some 
power of geotropic movement, there is not therefore an 
absolute distinction between the motor and sensitive regions. 
It should be especially noted that the occurrence of prolonged 
curvature in the hypocotyl does not disprove the existence of 
some independent geotropic sensitiveness in that part, it 
merely proves that sensitiveness is overwhelmingly present in 
the cotyledon. 
To those who wish to repeat the experiments, I recommend 
Sorghtim seedlings, as they are larger and more vigorous than 
Setaria , and give a higher percentage of corkscrew-like 
specimens. Phalaris also gives the result with considerable 
certainty. Most of the experiments were made in the dark, 
but some heliotropic experiments were made. It being 
known that the heliotropic sensitiveness is, in the species used 
(, Setaria , Sorghum , Phalaris ), either quite or nearly confined 
to the cotyledon, it is clear that the same sort of continued 
curvature ought to be obtainable by one-sided illumination. 
For this purpose seedlings were fixed on a klinostat in such 
a way that they were heliotropically stimulated, though removed 
from the action of gravity. 
Under these conditions they bent over to the light and 
continued curving just as in the case of the geotropically 
affected plants. But it is not easy to cultivate the seedlings 
on the klinostat, and probably on this account the heliotropic 
experiments did not give such good spirals as those obtained 
geotropically. Fair results were also obtained without a 
klinostat. 
As a control, seedlings were also grown on a klinostat in 
a dark room ; under these circumstances the seedlings should 
remain straight. In the first trials this was not the case, and 
this may possibly have been due to my having examined 
them too often with a light. 
When the jar in which the seedlings were contained was 
wrapped in black cloth and the klinostat kept in the dark 
room, the curvatures were almost absent. But this question 
