ADULT ANATOMY OF WELWITSCHIA MIRABILIS, 335 
the xerophyte house at the Botanic Garden, the soil conditions cannot but be somewhat 
different; hence the production of the fibre-like rootlets for the absorption of the small 
amount of moisture thus presented to the root. Tt is probable that in this plant the 
formation of lateral roots is conditioned by the amount of moisture present. 
Anatomy of Forking Root.—The anatomy of the normal elongated root and hypocotyl 
of Welwitschia has been described by other authors *, and full accounts have been given 
of their external appearance and internal structure and of the development of the ground- 
tissue, lignified fibres, &c. I have little further to add to their descriptions. 
The forked root system described in the young seedling (Pl. 34. tig. 1) is, however, 
of some interest and seems worth a short description, since it affords an excellent 
illustration of the powers of endurance of this remarkable plant. 
Text-fig. 2 (p. 336) represents a series of transverse sections from above downwards 
through the region of the root injured by contact with the stone. In text-fig. 2, A, the 
transition from hypocotyl to root structure is not quite complete, and the two groups of 
xylem in the stele are each monarch; while attached to each are two separate groups 
of secondary xylem and phloem, from which the normal diarch plate of the root has not 
Yet been formed. Just above the place of injury it is seen that the secondary xylem 
and phloem of both poles of the root are laid down in four groups (text-fig. 2, B); the 
first sign of disturbance is seen in one of the protoxylem groups (4), which becomes 
elongated and ivregular in appearance. The small bundle (c') seen in connection with d 
in A, has died out; but the small bundle c in connection with group a is still present, 
accompanied as before by two others. 
Immediately after the appearance of this irregularity in the group of protoxylem 5, 
the whole group is destroyed, and this half of the vascular tissues is represented only by 
à decayed mass (b, text-fig. 2, C). : 
The other and larger plate a, with its small secondary bundles, still persists. The faet 
that similar small bundles are not present in connection with the plate 4, as they are in 
all normal seedlings, shows that the injury to the root on that side must have taken 
place at an early stage before the age at which the additional peripheral bundles could 
have been laid down. 
The single remaining protoxylem group is now surrounded by four large and several 
smaller groups of secondary xylem and phloem. The peripheral smaller groupe cf 
outwards, evidently in another attempt to supply a branch. This attempt — 
however, with the same fate as the first, and another dead plate of vascular tissue 
thus results (e, text-fig. 2, D). : 
The four aes are now arranged symmetrically round the group of p f 
Xylem, and the root makes a third attempt: it divides at right angles to the plane ^ p 
two previous divisions, and a small portion of the vascular tissue is separated off pn. 
the larger portion which remains in the original main root. cue Tos thus gem : 3 
Successful in its development, but a small part of the remaining tissue subtending the 
tootlet in the main root is destroyed (d, text-fig. 2, E & F). 
* Hooker, Bower, Bertrand, U. cc. " 
+ See Bower, I. & IL. ; also text-fig. 3 of this paper, p. 342. 
SE ie 
