FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS, 593 
12. The vascular system at the apex of the plant is so arranged 
as to keep up the following direct vascular connections : 
(a) Between the leaf, and both peripheral and central parts of 
the stem. 
(4) Between leaf and crown. 
(c) Between stock and crown (cauline bundles). 
No fundamental change takes place in these relations as the 
plant develops. 
13. Increase in number of bundles at the base of the leaf is 
effected at first while the leaves are young by the development 
of fresh bundles at the margin of the leaves, but later by inter- 
calation of new young bundles between the older ones, and the 
successive peripheral rings of bundles in the stock correspond to 
the successive series of bundles thus intercalated. 
14, The development of the fertile branches is adventitious 
and exogenous. ‘Their vascular system is directly connected 
with the network of bundles which ramify below the surface of 
the leaf groove. There is no direct connection between the suc- 
cessive series of fertile branches and the successive rings of peri- 
pheral bundles of the stock, though both probably owe their 
serial development to the same causes, 7.¢. alternating periods of 
activity and dormancy of the plant. 
15. Spicular cells are developed from single cells of the 
parenchyma. These undergo apical growth, pushing their way 
between the surrounding tissues. They often follow the inter- 
cellular spaces. ‘Their walls are differentiated into an outer 
cellulose layer and an inner later developed lignified layer. The 
crystals of calcium oxalate lie between the two. The lignified 
wall is pitted. The cells remain uninuclear. 
16. The sieve tubes have their sieve plates collected on their 
sloping ends ; here and there a sieve plate is found on their sides. 
Postscript.—Since the above paper was written there has 
appeared in ‘ The Gardener’s Chronicle,’ August 13th, 1881, an 
account by M. Naudin of fresh observations on young plants of 
Welwitschia mirabilis, which seem to show that the type of 
development, which is constant in the specimens which I have 
had the opportunity of observing, is not the only one for this 
remarkable plant. In all my specimens the series of members, 
as above described, has been—(1) two cotyledons present in the 
mature embryo, (2) two plumular leaves decussating with these, 
and capable apparently of indefinite growth, (3) two structures 
which appear between these, and which, for reasons given above, 
I regard as buds in the axils of the cotyledons, (4) apical cone of 
the whole plant, which does not develop further. I gather 
from M. Naudin’s description that there may be another and 
