FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS. 587 
bundles in the lower part of the stock. It has been described 
by Hooker (p. 14) how in the stock and root of old plants the 
peripheral bundles are arranged in rings. The outermost of 
these rings is the youngest. This is the natural result of a 
process of continued intercalation of fresh bundles of the leaf 
trace as above described, followed in each case by a curvature of 
the newly-formed bundle out of the plane of the leaf trace into 
the peripheral part of the stem: and since before this curvature 
each new bundle proceeds a shorter distance towards the centre 
of the stem than the next older bundles, it will appear in trans- 
verse section of the stem nearer the circumference of the section 
than they. A similar explanation of the arrangement of bundles 
may be given for the crown; here, however, the bundles are less 
regularly arranged. 
Immediately below the surface of the lips of the leaf groove 
is to be seen a very complicated network of anastomosing 
bundles, usually of small size. These are represented in fig. x1, 
which includes the lower lip of the groove. I did not observe 
any blind endings of these bundles, though such endings may 
exist. Still to prove this is very difficult, since the bundles 
pursue a most tortuous course. A similar system of bundles is 
found at the periphery of the crown. ‘These bundles are accom- 
panied by tracheids with reticulated walls (v’ Mohl’s “ transfu- 
sions Gewebe ;” ef. Strasburger, ‘Coniferen,’ p. 99). In old plants 
these bundles attain a considerable size, so that they can easily 
be recognised with the naked eye. Further from the lip, most of 
these bundles join some few main trunks, which pursue a more 
regular course, and finally join the descending bundles of the 
leaf trace. But all of them do not end thus. As before men- 
tioned the corky degradation of tissue at the apex of the 
plant often includes vascular bundies, and this is especially 
common in older plants. It is certain of these ramifying bundles 
which are thus included in the degraded tissue. 
We have seen in my former paper that in the earlier stages of 
development the vascular system of Welwitschia does not differ 
greatly from that of other allied plants. The primary structure 
of the root corresponds closely to that of Hphedra, while the 
arrangement of the bundles of the hypocotyledonary stem presents 
no very remarkable peculiarities, It is only when the plumular 
leaves begin to develop that the vascular system assumes an 
arrangement peculiar to this plant. Still it is interesting to 
trace, even in plants of considerable age, how close is the corre- 
spondence in arrangement of bundles to that described in my 
former paper on the seedling of the plant. 
In the root the secondary thickening proceeds at first in the 
normal manner, and though, as the age increases, fresh peripheral 
