FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS, 589 
mation more or less like that of Welwitschia, and it is perhaps 
in these plants that we may hope to find the closest similarity of 
vascular arrangement to that in Welwitschia, which appears at 
present unique, and more especially so at the upper part of the 
plant. 
Development of Fertile Branches. 
The origin of the fertile branches is a point hitherto unobserved. 
I have been supplied from the Kew collections with material for 
the study of the development of the male branches. Since the 
position, appearance, and structure of the female branches is 
similar to these in the mature state, we may, for the present, 
assume that they resemble them also in their mode of develop- 
ment. 
The development begins at some distance from the base of the 
leaf groove, and usually on the inner lip of the groove, though 
exceptions to this rule are cited by Hooker (p. 20). The point 
at which the development of a fertile branch is about to begin 
may be recognised externally as a dark dot, the change of 
colour of the tissues at that point being due to the increase in 
the quantity of starch and protoplasm which they contain. 
First there appears a ring-like depression of the surface (fig. 
x11, 1); this depression deepens, while the central part enclosed 
by it grows on (2). As the development proceeds, that part 
of the ring furthest from the base of the leaf groove is more 
depressed than the part nearer to it. The result of this is that 
the central cone, which assumes the functions of the apical cone 
of the young branch, is turned upward (3, 4). The apex 
of the cone does not rise above the level of the surface of 
the lip, and it is thus protected during its early stages from 
pressure of the plumular leaf. The tissues surrounding the 
depression grow meanwhile more rapidly, so that the apex of the 
young branch is gradually arched over by flaps of irregular shape, 
which give to the branch, when seen from above (fig. x11, 5), an 
appearance as though it had been developed endogenously, and 
were breaking through the external tissues. This appear- 
ance remains after the branch has finally developed, the base of 
it being surrounded by an irregular margin (fig. xtv). Leaves 
are produced laterally on the apical cone of the young branch; 
these appear in successive decussating pairs, the first pair being 
anterior and posterior. The process of extension I have not been 
able to trace, but there is no doubt that it begins below the 
lowest pair of leaves, since (1) no traces of leaves are to be 
found at the base of the mature fertile branch, (2) the lowest 
pair of leaves of the mature branch are in the same position 
relatively to the plant as the first pair developed on the young 
