DR. J. D. HOOKER ON WELWITSCHIA. 33 
mass and becoming entangled with the cellular substance of the cone above it. I have 
made many dissections of the embryo-sac at about this stage, and before it, but have 
failed to detect any cells of the endosperm set apart, as it were, for this purpose. I find 
the whole endosperm-mass at the now open mouth of the sac to consist of loose or 
slightly coherent transparent ovoid utricles, with dark contents, of which many elongate 
upwards, and many do not. Of those which elongate, some, towards the centre of the 
mass, are quite free; others, towards its margin, remain firmly coherent to the denser 
tissue of the margins of the endosperm-mass. The central ones become the secondary 
embryo-sacs, and correspond to the corpuscula of Conifere and Cycadee. 
At Plate X. fig. 3, a few of these secondary sacs are seen protruding from the embryo- 
sac; at figs. 5 & 7 they are still further developed; and above fig. 5 is represented a 
small portion of the endosperm-mass, from immediately above the main body contained 
in the sac. At fig. 6 some of the young secondary sacs are shown, all the surrounding 
endosperm-mass being cleared away. 
. Though at first entirely resembling the other cells of the endosperm, the secondary 
sacs rapidly assume a different character, become tortuous, often inflated in parts, and, 
when preserved in alcohol, contain very diffused amorphous contents, together with 
minute globular vesicles, which turn bright yellow with iodine. Some of the transition 
stages are represented at Plate X. fig. 8. 
There next appear, in the substance of the cone of the nucleus, interrupted dark lines, 
radiating upwards and outwards from the summit of the embryo-sac. The lower portion 
of the embryo-sac is still quite evident, and may be readily withdrawn from around the 
endosperm, which forms an oblong body, pendulous from the base of the cone. The 
endosperm-mass is oblong (Plate X. fig. 9), its cells are well defined, and the outermost of 
the upper series cohere with the tissue of the cone above. A dark area now occupies 
the base of the axis of the cone, consisting of a tissue intermediate between that of the 
cone and of the endosperm-cells; and within this tissue the secondary embryo-sacs lie 
(Plate X. fig. 11), being, as it were, lifted out of the mouth of the sac by the interstitial 
erowth of cells therein. 
The secondary sacs are now elongated, club-shaped, membranous, with rounded 
apices and bulbous bases (fig. 12), in which are very opaque amorphous contents; trans- 
parent globules abound in the upper part: they vary in number from 20 to 40 or 60, 
are nearly erect, and radiate outwards, their bases being in close contiguity. 
As the nucleus elongates with the growing sac, it contracts at the base into a broad 
stipes ; and vascular cords, either simple or branched, traverse it on each side. - In some 
nuclei it happens that there is an apparent arrest of development of the endosperm ; this 
I found to be the case in many of Mr. Baines’s specimens, where (Plate IX. figs. 18, 19) 
the endosperm forms a flat tongue-shaped body in which the cells were irregularly deve- 
loped (fig. 25), very loosely invested by the embryo-sac*. There are, however, in the various 
* In the cavity of these embryo-sacs, which were not filled by the endosperm, I fancied I detected a filamentous 
net-work, resembling a very delicate cellular tissue. At the time, I was at a loss to explain it; but in looking over 
Hoffmeister's valuable work on the Higher Cryptogamia, I find a structure described in Pinus, which, if my obser- 
vation was correct, may throw some light on it. In this genus, at one period, when the endosperm-mass is much 
VOL. XXIV. F 
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