Conducting Tissue-System in Bryophyta. 21 
starchy tissues, in plants kept shut up in a tin box for a 
fortnight. 
The rhizomes of the different species of Polytrichum, accord- 
ing to Bastit, are all built up on fundamentally the same type, 
and this certainly holds good of the species we have examined. 
P. juniperinum and P. formosum (Fig. 19) come very close 
to P. commune , but are smaller and with rather less well 
differentiated tissues. The hypodermal strands are certainly 
less massive and with thinner walls, while the cells of the 
inner part of the radial strands are frequently only to be 
distinguished from the adjacent cortex by their smaller 
diameter, especially in P. juniperinum. The furrows are on 
the whole shallower, and hydroids very frequently abut on 
the endodermis. The outlines of the hydroids are strikingly 
angular in transverse section, and the angles where the thin, 
very oblique end-walls are inserted are frequently re-entrant. 
In P. juniperinum the thickness and lignification of the 
walls of the stereids decrease gradually as the periphery is 
approached, while the diameter of the cells increases, so that 
the living cells bordering the endodermis are often quite 
wide. In P . formosum the diameter of the stereids is more 
constant throughout, but their lignification and the thick- 
ness of their walls fall off in the same way. In neither 
case is it easy to separate a distinct pericycle. Differen- 
tiation of the conjunctive has not progressed so far as in 
P. commune. 
P. piliferum is much smaller and with much feebler tissue- 
differentiation. The hypodermal strands are little developed 
and in places not distinguishable on transverse section. The 
inner cells of the radial strand are scarcely distinguishable 
from the adjacent cortex. The furrows are much shallower, 
sometimes hardly distinguishable. The hydrom - stereom 
strand is small and often irregular in outline. The stereids 
are fairly thick-walled but very variable in diameter, the 
peripheral ones being quite wide. The hydroids are very 
few in number, of the same type as in P. juniperinum and 
formosum. 
