270 MR. J. R. VATZEY ON THE ANATOMY AND 
peripheral zone of cortical sterome is much deeper than in 
Atrichum (Pl. XI. figs. 28, 29, Pl. XII. fig. 47), being six or 
eight cells deep. These cells are sometimes, as in P. formosum 
(fig. 47), slightly separated by small intercellular spaces. It is 
probable that this is true generally, but it is difficult to make 
out, as, from the smallness of their size, very thin sections are 
required to show them. 
The cortical parenchyma is four to six cells deep, the cells 
being separated by very large intercellular spaces, so that the 
central strand appears in transverse section to be suspended 
by a number of chains (P1. IX. fig. 29) from the cortical 
sclerenchyma. 
The central strand is surrounded by a sheath similar to that 
in Atrichum. The leptophloém is much more largely developed 
than in Atrichum (figs. 28, 29), being from four to six cells deep as 
against one or two; the innermost cells of the leptophloém 
have a much smaller internal diameter than the more external 
ones, and are very much thicker-walled (figs. 29, 30). In con- 
sequence of this difference in thickness of the cell-walls there is 
an apparent separation of the tissue into two layers—an outer 
one, consisting of large (comparatively large) thin-walled cells, 
and an inner, consisting of thick-walled cells of small diameter. 
The leptoxylem consists, as in Atrichum, of a solid axial cylin- 
der of thin-walled cells, sharply distinguished from the innermost 
thick-walled cells of the leptophloém. The actual thickness of 
these cell-walls is rather greater than in Atrichum, and instead 
of their internal diameter being on the whole smaller than 
that of the adjacent leptophloém-cells, it is greater. The lepto- 
phloém has the same structure in other points as in Atrichum, 
containing protoplasm and nucleus. The prosenchymatous ends 
of the leptoxylem-cells are best seen in transverse sections, 
stained with either hematoxylin, Schulze’s solution, or methylene 
blue. 
In Polytrichum, as mentioned above, the theca is differentiated 
into two organs, namely, the sporangium and the apophysis. 
The sporangium has in this genus a more complicated structure 
than in the rest of the Order, being of prismatic form with from 
four to six sides. The apophysis has the form of a flattened 
bilaterally symmetrical spheroid (Pl. IX. figs. 1, 3, 4), attached 
by one pole to the seta, and by the other to the sporangium, in 
P. piliferum and P. commune. The exact form of the apophysis 
