FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS, 573 
witschia corresponds to that of Ephedra (cf. Van Tieghem, La 
Racine, p. 211). 
Meanwhile a further development has been going on in the 
parenchyma which surrounds the vascular tissues: this results 
in the formation (a) of a number of irregularly arranged spicular 
cells (sp. c.), whose axes are parallel to the longitudinal axis of 
the root ; (4) of long sclerenchyma fibres with no crystals in their 
walls (se/. 7., cf. Hooker, l.c., p. 15). The spaces between these 
are filled with thin-walled parenchymatous tissue, whose cells 
retain their cell nature, and play an active part in the further 
development (cf. below). At the periphery of the section lies 
a layer of cork derived from a phellogen layer, as already 
described. Since the same is the case in sections from older 
roots, the fact will not be again mentioned. It may be noticed 
that the cork in fig. 1 has at certain points attained a considerable 
thickness ; this corresponds to the fluffy layer already mentioned. 
No secondary free vascular bundles are to be seen in fig. 1, 
which represents a section cut far down the root of the youngest 
plant in the Kew collections. Thus far the structure presents no 
great peculiarities. The same root was, however, cut about one 
inch further from the apex, and by comparison of a series of 
sections, the first secondary bundles were observed to originate in 
the following way :—One of the cambian bands becomes laterally 
extended (fig. 11., 1), then a plate of parenchymatous tissue is 
intercalated between the extension and the main mass (fig. 11, ii.). 
A separate bundle is thus formed by branching of the main 
bundle ; it is, therefore, a direct derivative of it, and does not end 
“blind” (cf. De Bary, ‘ Vergl. Anat.,’ p. 303, &.). As the 
new bundle pursues its course up the root it leaves its original 
position relative to the main bundle system and takes a spiral 
course till it is placed opposite to one of the protoxylem masses 
(fig. 11, 41, 4,). A similar development goes on at the opposite 
side of the root, and a symmetrical arrangement is thus attained. 
It must, however, be remarked that the central bundle system 
of the roots of Welwitschia is not always arranged as regularly 
as here described, though this seems to be the typical arrange- 
ment.! 
This arrangement of the central vascular bundles of the root 
is well seen in the section represented in fig. 1v. This was taken 
at a point far down the root of the plant (fig. 11). This root 
1 The description which follows is mainly derived from the study of one 
plant which was handed over for dissection from the collections at Kew. 
It is represented in outline in fig. 111, i, ii, From a comparison of it with 
other rather younger plants, it is seen that the swelling of the stock starts 
near the top, and proceeds downwards, the lower limit of the swelling 
being pretty strongly marked, as seen in fig. 111, i. 
