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DR. J. D. HOOKER ON WELWITSCHIA. 41 
Cycadee, Dammara, some Podocarpi, and other Conifere. This venation favours the 
early splitting up of the leaf into innumerable lacinise—an arrangement that subserves 
ome purpose in the economy of the plant. 
The binary arrangement of its parts and bilateral venation of the floral organs of Wel- 
witschia are remarkable characters, and seem to be interrupted in the staminal whorl 
only (which is senary): thus, there are two leaves, two floriferous lobes, often two 
medullary axes in the root, a dichotomous panicle, decussating bracts to the cone, vas- 
~ cular cords in pairs in its rachis, two vascular bundles in each bract, two in the perianth 
of the female flower, two at the base of each ovule, two leaflets in each whorl of the 
hermaphrodite perianth, and two cotyledons to the embryo. | 
The general plan of the plant is that of a Dicotyledon, as the structure of its embryo 
indicates; the principal deviations being the straight venation of the leaves, the six 
stamens, and the isolated vascular bundles which are superadded to the generally exoge- 
nous vascular system of the stock and root. 
The male flowers are structurally hermaphrodite, and contain a naked ovule in the axis 
of the flower, which, though containing no embryo-sac, is provided with a very highly de- 
veloped stigma-like disc at the apex of the ovular integument. Welwitschia thus presents 
the hitherto unique case of a structurally hermaphrodite-flowered gymnospermous plant. 
The cones of Welwitschia are functionally unisexual, and the plant is probably truly 
dicecious; fertilization being effected by insects, before the nucleus of the ovule of the 
female flower is enclosed by its integument or by the perianth. 
The membrane of the embryo-sac, which is full of endosperm before fertilization, rup- 
tures or disappears at its summit; and the secondary embryo-sacs, which are developed 
at its apex, ascend into canals in the substance of the nucleus, where they meet the 
descending pollen-tubes, and are thereby impregnated outside the embryo-sac, and 
removed from it. 
After impregnation, the bulbous base of the secondary embryo-sac elongates, and 
descends into the cavity of the endosperm, when the germinal vesicle at its base gives rise 
by cell-division to a single suspensor, at the apex of which the embryo is developed. 
Welwitschia is a Dicotyledon and an exogenous exorhizal perennial plant, belonging 
to the gymnospermous group of that class, and having a very close affinity with both 
Ephedra and Gnetum, but differing from all previously known Gymnosperms in wanting 
the disc-bearing wood-cells, Notwithstanding this peculiarity, I place it in the same 
Natural Order with the above genera, and after Ephedra, of which genus it is the South- 
African representative. 
In its hermaphrodite flowers, its want of disc-bearing wood-cells, and in the impreg- 
nation of its secondary embryo-sacs taking place in the nucleus of the ovule exterior to 
the primary sac, Welwitschia is intermediate in character between angiospermous and 
eymnospermous plants. 
In common with Gnetwm and Ephedra, Welwitschia presents some very curious points 
of resemblance with Loranthacee and Santalacee, a further investigation of which will, 
I doubt not, lead to important discoveries, and to some further modifications of our 
accepted theories regarding the classification and morphology of flowering plants. 
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