41 6 Vines. — On Epinasty and Hyponasty. 
It must be pointed out, however, that whilst it appears 
from Frank’s observations that all dorsiventral members are 
diaheliotropic, it is not equally clear that they are all dia- 
geotropic ; in fact, this appears to be rather the exception 
than the rule. Frank, for instance, states that, in most cases, 
members which are more or less horizontal under normal 
conditions and when exposed to light, grow erect in darkness 
in consequence, as he suggests, of negative geotropism. He 
cites, as examples of this, the creeping shoots of Lysimachia 
nummular ia, Polygonum avicidare , A triplex latifolia , and other 
plants, radical leaves, and the thallus of Marchantia. 
The next paper to be noticed is that of De Vries 1 , which 
consists largely of a criticism of Frank’s theory of diahelio- 
tropism and diageotropism. The main contribution which he 
makes towards a knowledge of the subject is the fact that the 
growth of the two opposed sides of dorsiventral members is 
unequal, and that this unequal growth is apparently due en- 
tirely to inherent conditions. When the growth of the upper 
surface is the more active, DeVries terms the member epinastic ; 
when that of the lower, hyponastic . He observed that, as a rule, 
leaves are hyponastic at first, becoming epinastic in the latter 
part of their period of growth. 
De Vries’ contention, as against Frank, is that the assump- 
tion of peculiar forms of heliotropic and geotropic irritability 
in the case of dorsiventral members, is unnecessary and un- 
warranted by the facts. He endeavours to show that the 
various positions assumed by dorsiventral members can be 
accounted for as being due to various combinations of epinasty, 
hyponasty, negative or positive heliotropism or geotropism, the 
weight and balancing of the parts ; discarding altogether the 
idea of diaheliotropism and diageotropism. 
In his important paper on orthotropic and plagiotropic 
members, Sachs 2 touches upon this subject, and his views 
1 De Vries : Ueb. einige Ursachen der Richtung bilateralsymmetrischer Pflan- 
zentheile, Arb. d. bot. Inst, in Wiirzburg, I, 1874. 
2 Sachs : Ueb. orthotrope und plagiotrope Pflanzentheile, Arb. d. bot. Inst, in 
Wurzburg, II, 1879. 
