ADULT ANATOMY OF WELWITSCHIA MIRABILIS. 337 
is to be regarded as mesarch; Bower, however, in his study of the early development of 
the seedling, did not come to this conclusion and merely points out the fact that the 
protoxylem is * long drawn out ” *. 
Section III.—' Tur STRUCTURE OF THE RIDGES AND YOUNG INFLORESCENCES. 
Some of the most interesting facts disclosed in this investigation are concerned with 
the development of the vascular elements in the ridges on either side of the leaf-bases, 
and their connection with the bundle-system of the hypocotyl. 
General Structure of the Ridges.—In the young seedling (Pl. 34. fig. 1) the ridges, 
each as yet represented only by a small protuberant outgrowth (R), are made up of 
rapidly dividing parenchymatous cells, among which are scattered a few fibres with 
thickened and lignified walls: the epidermis is thin-walled and without stomata. 
In the older seedling, fibres become very numerous in both ridges, and cork-formation 
extends over the base of the outer ridge on its outer surface. Numerous stomata are 
present in the epidermis of the upper free portion of both ridges; these stomata resemble 
those of the mature leaf, and the epidermis (also like that of the leaf) is composed of 
conical cells with a thick cuticle impregnated with calcium oxalate. This region with 
stomata extends over the outer surface of the outer ridge for some distance towards its 
base, but stomata are absent on its inner surface, where it forms one side of the leaf- 
groove, and the epidermis is there made up of small, closely packed, cubical cells 
unprovided with a cuticle. Stomata and cuticle are similarly absent from that part of 
the inner ridge which forms the other side of the leaf-groove. 
Vascular System of the Ridges.—(a) In the seedling shown in Pl. 34. fig. 1 the 
vascular supply of the ridge primordium consists of a small group of bundles, which 
form a more or less concentric ring and end freely upwards (Pl. 35. figs. 15 a & b). | Each 
bundle composing the ring is collateral, and all its elements appear to be secondary in 
origin. No transfusion-tissue is present at this stage. When the bundles are followed 
downwards in a series of transverse sections, it is seen that while one or two from each 
group join on to the pairs of primary bundles in the hypocotyl, the greater number end 
freely in the parenchyma separating the two pairs from one another t. ; 
At this stage the inner ridge is as yet undeveloped, and there is no sign of a 
vascular supply either to it or to the cotyledonary buds. 
(^) In theolder seedlings, in which the outer ridge is elo j 
and the inner ridge is just beginning to be apparent, the latter has still no vascular supply, 
but the simple ring of bundles which formerly terminated at the base of the outer ridge 
has now undergone some considerable change. The central mass of parenchyma is 
greatly enlarged, and the bundles are widely separated from one another and are m 
irregularly distributed ; it can, however, still be seen that they constitute two series whic 
together form an ellipse, the bundles of the two series being orientated inversely vo one 
another, A good deal of transfusion-tissue accompanies all the bundles and is scattered 
ngated (e. g. in PI. 34. figs. 1a, 2) 
* Bower, I. p. 20, pl. 4. fig. 15, &e. 
s: . 3. F, G, H, p. 342. 
+ See text-fig. J, I, 3»2 
