588 F. O. BOWER. 
bundles are formed, still even in very old roots the primary xylem 
masses and the first products of secondary thickening may be 
observed with certainty. 
Passing upwards from the root to the hypocotyledonary stem, 
we have seen that in a plant of considerable age (fig. m1) the 
course of the primary xylem groups could be accurately followed ; 
that as we pass from the root upwards the two primary xylem 
groups separate; that each divides into distinct parts ; that these 
four parts could be traced into the hypocotyledonary stem, in a 
transyerse section of which there appears round each of the 
four primary xylem groups a number of secondary bundles 
arranged in a radiate manner. Comparing these facts with the 
observations recorded in my former paper on the seedling, it will 
be seen that the lower part of the plant retains for a considerable 
time an arrangement of the vascular tissues which is very closely 
related to that of the seedling. This grouping of the secondary 
vascnlar bundles round four centres corresponding to the original 
vascular bundles of the seedling may also be observed in plants 
of much greater age than thai represented in fig. ur. Sir Joseph 
Hooker observed and figured it, though, as the structure of the 
seedling was then unknown, the explanation of the fact was not 
obvious. 
As we approach the plumular leaves the arrangement of the 
secondary vascular bundles corresponds less closely to that of the 
primary bundles of the seedling, and seems to be determined 
rather by the form and position of the plumular leaves than by 
relation to the pre-existmg bundles. The vascular arrangement 
at the upper part of the plant having been fully described above 
need not be here recapitulated ; we must, however, for a moment 
notice the system of small frequently anastomosing bundles 
which is found immediately below the surfaces of the leaf groove. 
Those are, as far as I know, unique. They do not extend far, 
and appear as a rule to be thrown off with the masses of effete 
tissue which cover the apical part of the stock and crown. They 
appear, therefore, to be in the main a temporary system. It is 
with them that the vascular system of the fertile branches is con- 
nected, as will be stated below. 
Comparisons have been drawn between the bundle system of 
Welwitschia and that of other plants. For instance, Strasburger 
(* Conif. ti. Gnet.,’ p. 376) compares the stem with that of the 
Piperacee, Amaranthacee, and Nyctaginee, while De Bary 
(‘ Vergl. Anat.,’ p. 634) cites, in connection with it, the Cheno- 
podiaceze, Amarantacez, and Mirabilis, There are undoubtedly 
points in common between these and Welwitschia. It still 
remains, however, to investigate the structure of various plantg 
cited by Hooker and Strasburger as having an external confor. 
