Vines . — On Epinasty and Hyponasty . 425 
words, the leaf is hyponastic. This position is retained in 
darkness, both when the plant is in the normal position and 
when it is rotated on the clinostat. Under normal conditions, 
the leaves, as they develope, become epinastic ; the petiole 
sinks, and the laminae of the leaflets flatten out. Leaves in 
this stage of development show epinastic curvature in dark- 
ness, both in the normal position and on the clinostat ; but I 
have never succeeded in observing, in darkness, that transition 
from the hyponastic to the epinastic growth which is so 
marked in Primula , as the leaves of Vicia are apparently 
incapable of growth for more than a very short period under 
these circumstances. 
2. Observations on Hyponastic Members. 
In describing the foregoing observations on Primula and 
Vicia , I have assumed, without explanation, that the rising up 
of the youngest leaves of the former in darkness, and the 
position taken up by the leaves of the latter at their first de- 
velopment, are due to hyponasty. The only other possible 
supposition is that gravitation is the active cause. But, inas- 
much as these phenomena are equally apparent when the 
plants are rotated on the clinostat in darkness, it is clear 
that they cannot be due to gravitation. They are, in fact, 
spontaneous, and can only be ascribed to the more rapid 
growth of the lower side of the leaf, that is, to hyponasty. 
Still more convincing evidence of the spontaneous nature of 
hyponasty is, however, forthcoming. As the assumption that 
dorsiventral leaves are negatively geotropic seems to rest 
chiefly upon observations made upon radical leaves, I did not 
content myself with observing only Primula , but extended 
my observations to two other plants, Plantago media and 
Taraxacum Dens-Leonis , with the following results. 
Plantago media . A plant which had been growing fully 
exposed to light, the leaves of which were, consequently, ex- 
panded horizontally, was kept in darkness in the normal 
position for seventy-two hours. The young leaves gradually 
