FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS, 575 
before us, we may therefore consider it as probable that the 
peripheral series is connected terminally with the central group ; 
that is, that the bundles of the root form a single system having 
a common origin. 
To the question of the communication between the bundles of 
the central group and those of the peripheral system, I have paid 
special attention, since Bertrand (‘ An. d. Sci. Nat.’ série v, vol. xx, 
p- 10) asserts that the latter series are always separated from 
the central system by fundamental tissue. I have, however, been 
able to satisfy myself that the contrary is the fact, and by com- 
parison of long series of transverse sections, I have succeeded in 
tracing the passage of branch bundles from the central group to 
the peripheral series. As to the lateral communication of dif- 
ferent members of the same series, it occurs so frequently that it 
can be observed in any series of transverse sections ; moreover 
tangential sections demonstrate that the bundles of either series 
form a cylindrical network. It is owing to the irregularity of 
the frequent anastomosis that the central series, as well as the 
peripheral, show those varieties of arrangement to which they have 
already been described as being subject. 
As the root increases in age its bulk also increases. This is 
due partly to growth of the old bundles and formation of new 
ones, partly to growth of the tissues in which the bundles are 
embedded. 
It has already been stated that the bundles of the central group 
remain “ open” and increase in size, while fresh series of open 
peripheral bundles are formed outside them. The disposal of the 
members of the later-formed series is more regular than that of 
those earlier developed, so that in old roots the appearance is 
presented of a number of definite rmgs of bundles surrounding 
others less regularly arranged. The new bundles are formed by 
active division at certain points in the parenchymatous “ground 
tissue.” Fig. v represents the points of origin of three new bundles 
of a‘peripheral series. Though at first sight this figure gives the 
idea of a definite cambium layer in which the new bundles appear 
at certain points (as in the monocotyledonous stems with second- 
ary thickening), it will be seen, on observing it more closely, that 
at the limits of the figure the tissues bear traces of less active 
division, the fact being that the activity is specially localised 
around the point of origin of new bundles (cf. infra). 
The arrangement of the other tissues of the older root now 
demands further attention. The spicular cells seem here, as in 
other parts of the plant, to be pretty uniformly distributed ; they 
are more numerous towards the periphery of the root. Fresh 
spicular cells may be formed from single cells of the parenchyma 
at any point outside the vascular bundles; occasionally they are 
