574 F. 0. BOWER, 
being much older than those before examined, the bundles of the 
central system are further developed; it will be seen, however, 
that they correspond exactly in their arrangement to the descrip- 
tion given above. ‘The protoxylem masses can still be recognised 
though the protophloem masses cannot be traced. Around the 
former are grouped symmetrically four large vascular wedges, two 
of which are connected centrally with one another; these are 
derived directly from the activity of that cambium layer which 
appears between the protophloem and the primary xylem plate, 
those which alternate with them having been derived from them 
by branching, as above described. It is true there are frequent 
deviations from the type, due to the sinuous course pursued by 
the bundles of the centrai group, and by their frequent anasto- 
mosis both with one another and with the members of the 
later developed peripheral system; but the tendency is to return 
after these irregularities to the typical arrangement. Though 
in older roots the bundle system becomes complicated by the 
formation of large numbers of peripheral bundles, still as a rule 
the centre of the root is occupied by the original fourfold group. 
Since these bundles, and in fact all bundles of the root of Wel- 
witschia, remain “ open” for a long time, they attain in old roots 
a very considerable size. The discrepancy of this description 
with the figures and account given by Hooker depends upon the 
fact that the xylem is there omitted, while the phloem is repre- 
sented as the whole bundle (cf. also De Bary, ‘ Vergl. Anat.’ 
. 633). 
: On ey a the arrangement of the bundles of the central 
system comparatively, we see that there is here in the root of 
Welwitschia a case similar to that in the stems of many Dicoty- 
ledons, in which it is found that the broad medullary rays are 
traversed by intercalary bundles (Zwischenstringe, cf. De Bary, 
‘Vergl. Anat.,’ p. 408, &c.) ; these keep up a vascular connection 
between the primary bundles on either side of theray. We have 
as the counterpart of these intercalary bundles those branches 
(fig. Iv, 4,), which pursue a sinuous course along the very broad 
medullary rays of the root of Welwitschia, and which from time 
to time fuse laterally with the primary bundles. 
As the central group develops, there appear in the peripheral 
part of the root a number of fresh bundles, which, though not 
disposed regularly in rings, still show a tendency to that 
arrangement. Such bundles are to be seen in fig. Iv, per. bum. 
As to their ending I cannot speak definitely, but this much is 
certain, that whereas I have often been able to observe anasto- 
mosis between members of this peripheral series, as well as between 
them and the central group, | have never obtained evidence of 
their ending “blind.” Having the analogy of the central group 
