94 
F. 0. BOWER. 
from the first to the second type of construction, there is a 
sinking or lowering of the centre of construction; this is still 
more apparent if we pass on to those roots in which the 
stratified structure (Sadebeck) is more pronounced. In these 
types the centre of construction is situated at a still lower 
point; since the anticlinals cut the periclinal curves at right 
angles, it follows that where the centre of construction is more 
depressed, the sides of the apical cell or of the initial cells will 
be less inclined to one another, and more nearly parallel than 
is the case where the focus lies at a higher point, for instance 
in the apical cell itself. The figures of Schwendener clearly 
demonstrate that this is actually the case in the Marat- 
tiaceae, in which the initial cells appear almost oblong in 
longitudinal section. Lastly, it is clear that in our second 
type the initial cells may be represented to the mind as being 
gaps in the system of construction in just the same sense as the 
idea is applied by Sachs to the single apical cell. 
Having now defined the two extreme types of construction, 
it remains to compare with them the structure of the apical 
meristem of the root in the Osmundaceae, and especially in 
Osmunda regalis. The form of the apical or initial cells 
may fii’st be taken into consideration. In some cases a single 
pyramidal apical cell has been found, as in fig. 1, but longitu- 
dinal sections always show (figs. 11, 12, 19) that even where 
the segmentation is most regular the cell has a narrower 
and deeper form than in the roots investigated by Naegeli and 
Leitgeb, that is, the lateral walls are less inclined to one another. 
This points to a depression of the centre of construction, though 
so long as the single apical cell maintains the pointed pyramidal 
form that point must be within the apical cell. In connection 
with these examples, which conform more nearly to the first type 
of construction, those must be mentioned in which two pyra- 
midal cells are seen (fig. 16) which correspond not improbably 
to an arrangement like that in fig. 13, but cut in a plane oblique 
the initial cells, and, indeed, outside the tissue of the plant altogether. This is 
exactly the reverse of what is found in the Marattiaceous type of root- 
structure. 
