ADULT ANATOMY OF WELWITSCHIA MIRABILIS, 941 
from an older seedling (Pl. 34. fig. 1) intermediate in age between that figured by Bower 
in his first paper * and the youngest of those described by him in his second paper t. 
Text-fig. 3, A, shows the diarch root; in B the two poles of the root have separated, and 
in C two separate collateral groups of vascular tissue are present at each pole; the two 
groups are connected with one another by meristematic tissue (text-fig. 3, C, m) The 
levels at which these sections are taken can be judged by reference to the older seedling 
drawn in Pl. 34. fig. 4 b, where A indicates the upper level of the diarch-root structure 
and the stage at which the separation of the two poles of the root begins, and C is the 
stage corresponding with text-fig. 3, C. The four groups of vascular tissue present at 
this stage are continued upwards into the hypocotyl; they remain collateral past the level 
of the feeder (Pl. 34. fig. 4 b, E, and text-fig. 3, E), up to the level F in Pl. 34. fig. 4 b, 
when they become concentric. The formation of four concentric groups, characteristic 
of the upper portion of the hypocotyl of Welwitschia $, is gradually brought about by 
the addition of small secondary bundles round each of the four original main collateral 
bundles. The beginning of this process is seen at F, text-fig. 3, where meristematic 
division has spread outwards from each group and produced a large inner bundle (/) and a 
number of small peripheral bundles. In G and H, text-fig. 3, the gradual establishment 
of the four concentric groups is seen. It is these four groups (reminiscent as they are 
of the concentric steles of the Medulloseze §) which give to the vascular structure of the 
so-called “ stem” of Welwitschia its very striking appearance ||. 
One of these concentric groups is drawn in detail in Pl. 35. fig. 22. A number of 
isolated tracheids are scattered throughout the parenchyma in the centre of the group. 
A single and fairly regular row of cells defines the limits of each of these groups, but it 
was not possible either here or at any other level to make out any of the characters 
which distinguish a definite endodermis, so that it does not appear correct to designate 
them as * steles."' | 
In the short space intervening between levels G, I, text-fig. 3 (F and K in Pl. 34. 
fig. 4, b) f, the four separate groups are not so clearly defined. At I, text-fig. 3, the 
four main bundles have rotated on their own axes, and are now endarch ; in K, L, M 
is seen their further rotation and the division of each bundle into two, so that four 
bundles run up into each cotyledon. The other bundles which made up the concentric 
groups supply the plumular leaves, K, L, text-fig. 3. Each leaf thus receives at this 
stage a number of bundles, some of which have been connected with one cotyledon trace, 
some with the other. One leaf-bundle from each concentric group is at these stages, 
text-fig. 3, E-I, remarkable for its greater size, and it appears probable that these four 
bundles represent the original leat-supply, two to each leaf, before tho intercalation 
of the secondary bundles began. In older seedlings the ever-increasing numbers of 
leaf-bundles often become distributed in rings more or less concentrically arranged 
* Bower, I. pl. 4. fig. 15. + Bower, II. pl. 32. fig. 6. 
t Cf. the folding of the eambium in the bundles of the peduncles ; Sykes, 1910. 
§ Weber & Sterzel ; cf. Sykes, 1910, Phil. Trans. Roy. Soc. ined. | i. ; 
| Of. the four groups of vascular tissue in Convolvulus Scammonie ; Solereder, p. 512, fig. 131. 
*| In an older seedling the four hypocotyledonary groups were traced up to ? in. from the apex. 
