345 MISS M. G. SYKES ON THE SEEDLING AND 
Throughout the plant, except in the minute hair-like lateral rootlets *, there are also 
found wider elements, with three rows of bordered pits on their longitudinal walls, and 
having their transverse walls absorbed (Pl. 35. fig. 24 a, & Pl. 34. fig. 245) T, except for 
a small peripheral ridge T. 
Comparative.—Since all the main essentials of seedling structure are preserved in the 
adult Welwitschia, it is obvious that the most important comparisons with other plants 
are those already made with various seedlings. I know of no recent plants whose stem 
anatomy can profitably be compared with the anatomy of the hypocotyl in Welwitschia ; 
its whole adult structure is, however, strikingly reminiscent of that of the stems of some 
of the Medullosez. 
The four concentric groups of secondary vascular tissue, each with tracheids scattered 
throughout its pith, are very like the large central steles of Medullosa stellata and the 
smaller but more irregularly arranged steles of M. Solmsii, while the peripheral series 
of secondary bundles, arranged as they often are in several concentric rings, may be 
compared with the outer rings of secondary elements in M. stellata, var. gigantea, &c.{ 
Resemblances in other respects between Welwitschia and the Medullosez have been 
indicated by the author elsewhere ||. 
Section IX.—GENERAL CONCLUSIONS. 
1. The mature plant may well be described as an “adult seedling”; the main axis is 
differentiated into root and hypocotyl, and bears, in addition to the two cotyledons 
with buds in their axils, only two plumular leaves at the base of a deep groove. 
On either side of this groove there is a ridge made up of rapidly dividing 
parenchymatous tissue. A study of the development of these ridges shows that 
the outer ridge arises as a small projection between the margins of the cotyledon 
bases; the accelerated growth producing the projection afterwards spreads laterally 
and gives rise to the long ridge. Similar accelerated meristematic growth, at the bases 
of the cotyledonary buds, produces the inner ridge on which the inflorescences are 
usually borne. Further development in this region causes the apex to be completely 
buried by the enlarged cotyledonary buds or lobes of the crown. 
2. The small projection from which the outer ridge is developed receives at first 
a concentric ring of secondary bundles which end freely downwards in the hypocoty l. 
As the ridge grows, numerous additional bundles are intercalated, and secondary 
connections are established between the bundles of the hypocotyl and those of the 
ridges. The bundles of the inner ridge and inflorescences are connected with those of 
the outer ridge. 
3. Owing probably to the great length of the hypocotyl, the ¢ransition from the structure 
at the apex of the plant to the root-structure is remarkably slow. The two bundles of 
the diarch root fork and give rise to two pairs of bundles; each of these original pairs 
supplies one of the cotyledons in the seedling; they are still prominent even in plants of 
* Ante, pp. 334-5. + Cf. Gwynne-Vaughan. 
+ De Bary, p. 335; Bertrand, 1874, p. 16 (Ephedra and Gnetum). $ Worsdell, V. pp. 133, 134. 
|, Sykes, 1910, I. p. 625, and II. ined. ; cf. Worsdell on the Peduncle, IV. pp. 768-770. 
