pdf 25 MB - BSBI Archive

73 ON THE SEXUAL ORGANS OF THE CYCADACE^.
niistaken when I regarded (in tlie memoir quoted) the cavity of the
embryo-sac, which soon loses its membrane, as formed by absorption
and dilatation in the nucleus. The same error had ah'eady been com-
mitted by others in the case of the Coniferce, and the point has only
been cleared up by the researches of Pineau.
The free conical summit of the nucleus, in which I formerly looked
for the embryo-sac, is situated above it, and rests upon its membrane.
I considered as belonging to the nucleus a special vascular expansion
formed of bundles which, after penetrating the ovules, rise above the
external bundles, perforate the woody layer of the coat (producing the
holes in its base ;
see Plate XCI. fig. 16), and distribute themselves, by
ramifying and anastomosing, on the interior surface of the coat. They
terminate above just at the point where the nucleus becomes free ; it is
consequently blended with the coat for two-thirds of its height. I
had noticed this internal vascular system in all the CycadacerB, but it
escaped my notice at first that it exists previous to fertilization. It
has since been also made out in the CotiifercB.* Guided by analogy,
I considered myself justified in terming it an expansion of the cha-
laza.f 111 the ripe fruits it appears much more distinctly ; and when
the remains of the nucleus which cover it are reduced to a thin mem-
brane, as in Macrozamia and in a Cycad from New Holland, it is seen
through it, and produces reticulated impressions on the surface of the
endosperm. (Plate XCI. fig. 13 and M, fig. 15 and 17 ; Plate XCII.
fig. 11.)
As these e vuloc perforate the coat, and are situated between it and
the enlarged part of the nucleus, it seems that they cannot be regarded
as belonging to the coat. Heinzel (Diss, de Macrozamia) states that
the vascular network is included between two membranes ; but this
view does not seem altogether accurate, since these cellular lavers
* The analogue of these yascular bundles may be seen at the base of the
micleus in WelintscMa (Iloofcer ' On Welwitschia,' p. 33, tab. 9, fig. 11 and 12 ;
Trans. Linu. Soc. vol. xxiv.). Tliej become afterwards more developed (1. c. p.
37).
f Aim. des Sc. Nat. iii. p. 196. A vascular network which seems to be
of the same nature has been observed more recently in some Evjihorliacece. A.
Gris. has studied it carefully in liivinus. He also adopts the name ibr it of
expansion of tlie chalaza, and I am astonished that its resemblance to what
exists in the Cycadcan ovule has escaped his attention. Just as in it, the nucleus
is united to the coat, wjiich the endospei'm in its enlargement reduces by
compressio nto the state of a spongy membrane. (Ann. des Sc. Nat., ser. xv.
p. 1 pi. ii. fig. ; 8.)