18 DR. J. D. HOOKER ON WELWITSCHIA. 
these are four inches long, and about one inch at the broadest diameter: the largest 
I have seen are those of the specimens sent by Mr. Monteiro, which are two feet broad 
at the base. Dr. Welwitsch states, in his letter to Sir William Hooker, that the leaves 
attain a length of six feet; and according to Mr. Monteiro's letter (p. 4) they may attain 
even a larger size. I have no evidence of the plant ever bearing more than two leaves: 
there is, however, no reason why more than this number should not be developed ; for the 
embryo may occasionally be tri- or poly-cotyledonous, as is the case with so many other 
Gymnosperms, including its near ally Ephedra. In all my specimens, however, the 
appearance of more leaves than two arises from the splitting of one or both, and from 
subsequent interstitial growth of the tissues of the crown and stock completely sunder- 
ing these portions at their bases. "These disruptions may always easily be recognized, 
from their adjacent margins being ragged, and deprived of cuticle at a greater or less 
distance from the base, though as the severed portions grow outwards their newer parts 
acquire a rounded edge, covered with epidermis. 
The base of the leaf, which is retained within the groove between the crown and 
stock, is, in the dried specimens, excessively thin and almost membranous ; that this is 
not entirely, if at all, due to the shrinking of its substance is evident from an examina- 
tion of the tissues, of which the parenchymatous is almost suppressed, and the fibro- 
vascular reduced to very narrow cords. The exposed portion of the leaf is of a hard 
leathery consistence, greenish and glaucous on the upper surface, paler green, suffused 
with red-brown, on the under; it is pth of an inch in thickness, quite entire along the 
rounded margins, longitudinally striated on both surfaces, the stris; answering to in- 
numerable slender, close-set, narrow grooves. The nervation, which is parallel through- 
out, is scarcely distinguishable on the surface. 
The internal structure of the leaf (Plate XIV.) is beautiful and singularly complicated, 
well supporting the other evidence of its perennial duration. The outer walls of the 
epidermal cells (Plate XIV. figs. 1 & 2a) are horny and thickened, and their cavities 
have few contents. Beneath the epidermis of both surfaces is a thick layer of very 
lax, soft, cellular tissue (figs. 1 & 2 b), traversed longitudinally by bundles of liber (figs. 
1 & 20), and strengthened, as it were, by a confused mass of the rigid spicular cells 
(figs. 1, 2 d, & 4) covered with crystals, that have been described as abounding in the 
parenchyma of the trunk. These spicula are in this part of the leaf of a rather more 
definite shape, and are in a far more definite position relatively to the other tissues, than 
in the trunk; they do not either cross or intrude upon the liber-bundles, are placed 
perpendicularly to the surfaces of the leaf, and are often bent at a right angle at one or 
the other oreven at both ends. The tissue they traverse is so soft that its cellular 
nature is not very evident; and the effect of the spicula in holding this together is 
rendered obvious by pulling one with a pair of fine-pointed forceps under the microscope, 
when, owing to its curved form, rigid texture, and rough surface, it resists with- 
drawal without eomplete laceration of the surrounding tissues, at the same time often 
dragging other spieula with it, these being entangled together by their hooked or 
branched ends. | 
Towards the middle of the leaf is a thicker layer of ordinary parenchyma 
