pdf 25 MB - BSBI Archive

ON THE SEXUAL ORGANS OF THE CYCADACE^,. 77
liesion exists with the amniotic membrane). At this point a total
absorption of the membranes probably takes place, so that the policn-
tube can penetrate to the top of the corpnscles.
The nnfertilized corpuscles at this time appear entirely filled with
cellular tissne, or with a mass of protoplasm regularly divided by
vacuoles. With respect to this I do not feel quite certain, but when
the membrane is torn the included mass has pretty much the appear-
ance represented in Plate XCII. fig. 5. I have found the same slate
in fertilized seeds which possess a normal embryo. It is probable that
all the coi-puscles which exhibit it (Plate XCII. fig. 4) have remained
unfertilized ;
for I have always met with one or two at the same time, in
which a small group of larger cells, from which the suspensor originates,
could be observed free in the middle of the cavity. I imagine that
this group at first occupies the base of the cavity, and that it is
not till afterwards that it is elevated to a higher level by the pressure
of the suF'pensor. It jnay be that this displacement has been simply
the effect of the preparation which the object has undergone. The
membrane of the corpuscles is relatively dense and resisting, and by
transmitted light it seems composed of small cells with thick Avnlls
(Plate XCII. fig. 2 a, fig. 6, very much enlarged). I formerly stated
that this was actually the case (Ann. des Sc. Nat. 1. c. p. 198), and
Gottsche held the same view (Bot. Zeit. 1845, p. 400), but we have
really here what Schleiden has observed in the corpuscles of the Coni-
fers. The external surface of the cellular membrane of the corpuscle
is covered in its whole extent with a layer of very small cells, formino-
a kind of epithelium (Hofraeister, Vergleichende Untersuch. pi. 28
and 29). Gottsche has found the total thickness of the wall in Ma-
crozamia to be O'Ol mm. In ripe seeds the corpuscles are situated in
the upper part of the endosperm. They may be more or less flattened,
sometimes free above, at other times attached to the lower surface of
the areolae. When the top of the nucleus or dried cone is torn off,
the corpuscles usually follow with it, with the suspensors coiled up-
Avards by the embryo. I have not been able to ascertain if the cor-
puscles are perforated at the summit. In those which I look upon as
unfertilized, not a trace of opening can be seen. In those which have
been fertilized, the fragments of cells which have been already spoken
of (Plate XCII. fig. 8) are seen at the extremities. It is possible that
amongst these debris a passage exists for the pollen-tubes. I have,
VOL. VII. [aIARCH \, 1869.] G