APEX OF THE ROOT IN OSMUNDA AND TODEA. 
93 
sive segments are cut off from the lower ends of the truncated 
pyramidal initial cells, form part of successive periclinal curves. 
The number of periclinal curves may thus increase to a high 
figure ; there is, however, no corresponding increase in the 
number of layers of cells in the mature root beyond a certain 
point ; thus some at least of these periclinal curves must stop 
short, as would naturally be the case if the structure of the 
root were of the fan-like type, but maintained its cylindrical 
form. A second necessary consequence of the coaxial system 
of construction is that it would be impossible to trace the pro- 
cambial cylinder with a smooth outer surface up to the apical 
group, or in other words, that the pericambium could not be 
so traced as a continuous layer of cells, but would be composed 
of parts of successive layers. The same may or may not be 
the case for the epidermis, according as it is derived from 
portions of the lateral segments, cut off by an epidermal wall 
(as in the type described by Naegeli), or has a common origin 
with the root- cap from the cap-segments. Schwendener does 
not speak definitely on this point, but my own observations on 
Angiopteris indicate that the latter is the case. If it be so, 
then the epidermis must originate in a manner similar to that 
pseudo-epidermis described by Strasburger (‘ Conif and Gnet./ 
Taf. xxiv, fig. 26) in Taxus baccata; it would originate 
from portions of successive layers of the meristem, not from 
one acropetally continuous layer. It is to be further noted 
in connection with the scheme represented in fig. 34, that the 
focus of each successive periclinal, by which segments are cut 
off from the initial cells to form the body of the root, lies at 
the time of segmentation at a point below the group 
of initial cells. In the former type, however (fig. 33), it 
will be readily seen that the focus or centre of construction 
lies in the apical cell itself (Sachs, l. c.). 1 Thus in passing 
root of the second type above described, we have a case of four initial o 
apical cells, giving rise to all the tissues of the organ, while the resulting 
tissues are arranged on a coaxial or fan-like system. 
1 It will be interesting to observe in this connection that Sachs has drawn 
attention to the fact that in Fucus the centre of construction lies outside 
