340 MISS M. G. SYKES ON THE SEEDLING AND 
arranged into two groups: towards the base the series forms an almost continuous stele, 
It is not possible certainly to ascertain whether there be any primary elements in these 
bundles; but by far the greater number of their constituents are entirely of secondary 
origin. 
The group of bundles running up into a cotyledonary bud originates from the two 
bundles of the cotyledon in the axil of which the bud is borne: it is interesting to find 
that the vascular supply of the cotyledonary bud bears the same relation to that of the 
cotyledon as does the vascular supply of one of the flowers of the inflorescence or of one 
of the inflorescence-branches to the bract in the axil of which it is borne *. 
In the older cotyledonary buds—or lobes of the crown, as they are often called in the 
later stages—cork-formation has extended over the whole surface. The original vascular 
supply does not seem to have undergone much change t, except that the bundles forming 
the elongated series have become more or less separated from one another by the growth 
of the parenchyma, and may in some cases appear to be arranged inaring. At the base 
of the bud the inner ridge has now grown up T, and its bundles form a very irregular . 
ring round the original bundles of the bud (Pl. 35. fig. 18) ; they run in all directions, 
and in some cases they appear to establish connections with the bud-bundles. 
Section V.—TRANsITION PHENOMENA. 
I have now to describe various facts connected with the transition phenomena in 
Welwitschia, chiefly relating to the behaviour of the special bundle-system supplying the 
ridges. For this purpose it is necessary to give an account of the transition process in 
the main bundles, which traverse the root and hypocotyl and run into the cotyledons 
and leaves; this process is in itself of considerable interest in this plant, but Bower's 
clear description makes it superfluous to give a second full account, and I propose merely 
to give the outlines, laying especial stress on peculiarities which are here for the first 
time demonstrated, or which are important in the light of recent research. 
Outlines of Transition.—The main facts in the youngest seedling are as follows :— 
Two bundles enter from each cotyledon, and almost immediately rotate to form the four 
exarch collateral bundles of the hypocotyl. After a considerable interval, the proto- 
xylems of each pair fuse to form one of the poles of the root, the two phloems of the two 
groups thus produced remaining separate. Finally, one of the phloem groups from one 
pole joins one of the phloem groups from the adjoining bundle of the other pole, and 
there is thus produced a normal diarch root in which two phloem groups alternate with 
two xylem groups. There is no primary xylem in the hypocotyl, save that which passes 
out into the cotyledonary traces ; similar facts have been described in Araucaria §. 
Text-figure 3 (pp. 342-343) represents a series of transverse sections taken at intervals 
* Strasburger, 1872, pp. 144, 145. t Bower, II. pl. 32. fig. 9, p. 583. 
+ Bower, II. pp. 581, 582. Professor Bower’s material did not make it possible to distinguish between the 
original vascular system of the bud itself and those later-formed bundles supplying the tissue of the rapidly 
enlarging inner ridge, by the growth of which the lobes of the crown are upraised, 
$ Seward & Ford, 1906, pp. 333-336. : 
