34 DR. J. D. HOOKER ON WELWITSCHIA. 
specimens examined, great differences to be found in the relative size of the nucleary . 
cavity, embryo-sae, endosperm-mass, secondary embryo-sacs, and cone of the nucleus. 
As the endosperm-mass increases, it becomes hollowed out at the top, below the base 
of the cone, into a cavity containing loose endosperm-cells; and the body of the nucleus 
becomes reduced to a thick fleshy coat, on the sides of which the’ vascular bundles 
ramify but little. This endosperm, now densely cellular, is the whole albumen of the 
seed, and consists of a body of granular substance and a constricted collar or neck, of a 
very different, looser, more fleshy, but very elastic tissue, which surrounds the cavity, 
and coheres with the base of the cone of the nucleus above. 
The cone of the nucleus is next found to present an outer very cellular periphery, and 
an inner substance of much firmer, tougher tissue, traversed, along the dark radiating 
lines mentioned above, by many canals of various lengths and dimensions, which ascend 
outwards towards the periphery, to about two-thirds of the total length of the cone. 
Plate X. figs. 20-24 represent horizontal sections of a cone, taken at different heights, 
and show its loosely cellular epidermal layers of cells and dense interior substance, 
which is cancellated by these canals. The secondary embryo-saes have grown up- 
wards into these canals in great numbers, their bases being still gathered together, 
as it were, at the base of the axis of the cone, where they hang over the mouth of the 
cavity in the apex of the endosperm (Plate X. fig. 10). If the cone be now torn away 
from the top of the endosperm, and the tissues surrounding its base removed, the 
lower ends of these secondary sacs may be very easily exposed. | 
Fully formed secondary sacs taken out of these canals are shown at Plate IX. figs. 30, 31, 
and at Plate X. figs. 18, 14. These vary much in length and breadth, but always taper 
downwards, and are bulbous and very rarely branched (fig. 14) at the base. They are 
sometimes solitary in the canals, sometimes in twos or threes. When drawn out, they 
are often found to be longer than the cone itself, either from having been folded or 
from the canals being sinuous ; but, owing to the transparency of these secondary sacs, 
and the tough, elastic, opaque nature of the tissue of the cone, I have never been able 
so to lay a cone open as to see the undisturbed sacs in situ. The sacs are, however, 0 
large, so well defined, and so easily removed, that there is no difficulty in ascertaining 
their numbers, form, position, &c. with sufficient precision. 
Another change that occurs about this time is the separation of the tissues of the 
nucleus forming the walls of the seed, into two layers (Plate IX. fig. 19) around the upper 
part of the endosperm. Of these layers, which are both continuous with the cone above, 
the outer one is the denser; and the inner one, like that of the neck of the endosperm- 
mass, is so tough, elastie, and troublesome to sever, as to render it difficult to expose 
the base of the cone and the apex of the endosperm-mass without tearing away the latter. 
This splitting of the nucleary walls into two layers is shown at the base of the cone, in 
Plate IX. figs. 26, 27, 29. 7 
Development of Embryo.—At the period last described, and very often earlier, one or 
smaller than the sac, the inner wall of the sac is covered by a very delicate cellular endosperm-tissue, filling up the 
space between it and the previously formed endosperm. The representation of this tissue would answer not inaptly 
to the appearances I saw. (See Currey’s excellent translation, p. 408, t. Ix. fig. 4.) 
