STKTJCTURE AND AFFINITIES OF CALLITIMCHACE^. 37 
presenting a semilunar l-celled appearance, as if the cells liad become 
confluent, and this is equally remarkable in one species of Stilbe,^ 
The ovary Is, as described by Prof. Babington, dicarpous, the dorsal 
suture of each carpel projecting inwards and uniting with, the placenta, 
so as to make it 2-celled. The ovule is ampliitropal, the raphe not 
being more than half its length, and what is remarkable it scarcely in- 
creases in length as the seed ripens, so that in the matured seed it is 
scarcely more than a fourth of tlie length of the seed itself; and an- 
other peculiarity is, that the nucleus aud subsequently albumen incom- 
pletely distend the tunic at the upper part of the inner side next the 
placenta, and in the ripened seed a membranous portion of the tunic is 
left in that situation, like a poiiion of a wing. The radicle is distant 
from the hilum by nearly half the lengtli of the seed, so that, together 
with the shortness of the raphe, the seed differs considerably from tliat 
of the Eaphorhiaceie, with whicK Callitriche has been compared. The 
embryo is nearly as long as the albumen and almost half its diameter, 
and the cotyledons are about one-third of ihe length of the em- 
bryo itself, so that in these characters it does not differ much from 
ElatinaceiB and CaryophjUace^, And another circumstance in which 
Callitriche agrees \\\i\\ElatinQce(jB is, that the achcninm or half-carpel, 
when growing separately, so that it can take its natural form, becomes 
curved in the same manner as the seeds oiElaVine. This curvature, 
as in other similar cases, is owing, there appears no reason to doubt, 
to the curvatvn-e of the seed, not of its cai']:)ellary coveriug. 
It appears that botanists are undecided as to whether the ovule at 
the time of flowering has a coat, or consists only of a naked nucleus, 
Dr. Ilegelmaier having very recently in his valuable monograph on 
CalUtriche advocated the latter opinion. Whether a tunic is present 
at the earliest stage at which the ovule is distinctly visible I am unable 
to say, and take it for gi'anted it is to that period at which the nucleus 
and tunic may not have become differentiated to which Dr. Hegelmaier 
alludes ; but in C. cenw, at that time which appears to be the flowering 
stage (the flowers being unisexual, the flowering stage in the female 
cannot be exactly defined) the ovule has a distinct, nearly transparent 
♦ I hare never been able to find any trace of a petal in the female flowers of 
these two genera, although of the latter I have examined some in an early 
ptage, apparently some time before flowering. I therefore conclude that the 
feuuile flowera of HVhacece are apetaloiis, and this would diminiali the dLstauce 
between Callitriche and Slilbe, 
