Vines . — On Epinasty and Hyponasty. 431 
I may note, in passing, that Krabbe assumes that the leaf 
of Dahlia is negatively geotropic, and he does so for the 
following reason. He observed that the leaf does not exhibit 
epinastic curvature when in the normal position and exposed 
to light, whereas it does exhibit this curvature when exposed 
to light on the clinostat. From this he concludes that the 
heliotropic effect of light is insufficient, by itself, to counteract 
epinasty; and that the horizontal position of the leaf under 
normal conditions is due to the combined influence of light 
and of gravitation in opposition to epinasty, the latter, as he 
suggests, producing a negatively geotropic effect. The facts 
do not, however, justify this conclusion. They may be 
accounted for on the assumption that the light to which 
Krabbe exposed the plant in his clinostat-experiments was 
not sufficiently intense to induce the full heliotropic effect. 
But apart from this assumption, his observations only prove 
that gravitation has some effect, though the facts give no 
indication of the nature of the effect. In accordance with 
what I have stated above, I believe the effect of gravitation in 
Dahlia to be diageotropic, and I would point out that Krabbe’s 
observation can be explained quite satisfactorily from this 
point of view. 
With regard to hyponastic members, it may be assumed 
that here also there are three forces which determine their 
position : their own hyponasty ; the action of light ; the 
action of gravitation. The tendency of hyponasty is to raise 
the member so that its long axis approaches the vertical. 
The effect of light is, as in epinastic members also, to bring 
and retain the member in the horizontal position — that is, 
it is, I believe, diaheliotropic. The effect of gravitation is, as 
I have clearly proved, certainly not to produce negatively 
geotropic curvature, but is probably diageotropic. 
I have made some experiments on hyponastic members, 
similar to those on epinastic members described above, with 
the object of ascertaining whether or not they are diageotropic. 
A normal plant of Plantago media , growing in a pot, was 
placed in darkness with its long axis horizontal. Of the 
