16 DR. J. D. HOOKER ON WELWITSCHIA. 
required. Had the embryo presented any monocotyledonous character, as the develop- 
ment of adventitious roots from its radicle, or had it possessed but one cotyledon, then 
it is to be assumed that the future plant would have been unsymmetrical, and either a 
further deviation from the exogenous plan or a decided transition to the endogenous 
might have been expected. 
Its discoverer affirms (see p. 2), but on what grounds he does not state, that the two 
leaves of Welwitschia are the developed cotyledons of the embryo: of this there is no 
absolute proof forthcoming; nor can there be any, short of watching the process of ger- 
mination. But much may be inferred from the anatomy of the trunk; and all that 
has been there observed is entirely in favour of Dr. Welwitsch’s statement. For, 
firstly, there is the obvious fact, that the leaves of the youngest specimens as well 
as those of the oldest all occupy precisely the same position in relation to the axis and 
cambium-layer; secondly, there is the difficulty of accounting, under any other supposi- 
tion, for the single transverse vascular stratum, whose bundles are continuous with those 
of the leaf at every period of growth; thirdly, the absence of anything like an inter- 
node in the axis; lastly, the uniformity with which the definite bundles are given off to 
the erown and stock, and the condition of the tissues within the lips of the transverse 
groove, both indieate one continuous leaf-formation from the very earliest epoch in the 
plant's life. 
Nor is such a development wholly without its counterpart; for a very analogous case 
is presented by another Dicotyledonous South African genus, though occupying a widely 
different position in the natural system. I allude to the cases of Streptocarpus polyanthus 
(Hook. Bot. Mag. t. 4850), S. biflorus, and S. Rexii, whose germination has been observed 
by Mr. Crocker at Kew, and his account of which was read before this Society, and 
published, with illustrations, in our Journal (vol. v. p. 65, t. iv.)*. In these plants the 
minute, terete, exalbuminous embryo has two short cotyledons, of which one becomes 
developed in germination into the great oblong penniveined leaf of the future plant, 
which, like those of Welwitschia, lies along the ground; the other cotyledon soon dis- 
appears, and the radicle developes a short caulicle terminated by rootlets. The inflo- 
rescence of Streptocarpus is adnate to the petiole and base of the midrib of the leaf, and 
consists of a depressed axis, giving off a succession of many-flowered scapes from its 
upper surface. Here the caulicle answers to the stock of Welwitschia, the adnate por- 
tion of the inflorescence to the crown, and the scapes to the peduncles. But whereas 
Welwitschia is a perennial symmetrical (bilateral) plant, of which both cotyledons are de- 
veloped, Streptocarpus is an annual (or biennial) unsymmetrical (unilateral) plant, of 
which but one of the cotyledons is developed. 
It is perhaps a fanciful idea, but worth recording, that the mode of growth of both 
these plants may have originated in a conformity to conditions, inasmuch as Wel- 
* Some months after the publication of Mr. Crocker’s paper, it was found, from a statement in the ‘Revue 
Bibliographique’ of the Botanical Society of Paris (vol. vi. p. 148), that the same fact had previously been recorded 
of * polyanthus and S. Rexii by Dr. Caspary, who published it, in 1858, in the * Verhandlungen des naturhis- 
torischen Vereins d. Preuss. Rheinlandes u. Westphalens,’ xv. Jahrg., pp. 74, 75. 
