Conducting Tissue-System in Bryophyta . 1 5 
transverse section, but is more often triangular with rounded 
corners and slightly convex sides, is covered by a small-celled 
and rather thick-walled surface-layer, which bears the long, 
thick-walled, and very brittle rhizoids, often in such great 
numbers as to form a dense matted investment, as thick as 
half the diameter of the rhizome. The scales described by 
Bastit are attached to the projecting corners or ridges. We 
have not been able to make out the exact distribution of the 
scales, but they appear to be inserted at considerable intervals 
along the ridges. Their structure is well described by Bastit 
(op. cit., pp. 352-5, Figs. 44-6). We did not succeed, how- 
ever, in the midrib of the scales borne by the rhizome proper, 
in distinguishing his ‘bundle’ from his ‘hypodermic zone.’ 
We find that the midrib consists entirely of elongated thick- 
walled cells, continuous with those of the hypodermal strand 
occupying the ridge to which the scale is attached (Figs. 13, 
14). Of Bastit’s ‘ cellules allongees en forme de tibia’ (p. 354), 
evidently equivalent to Haberlandt’s ‘ siebrohrenartigen Zell- 
reihen,’ we can find no trace in these scales. Possibly Bastit’s 
description refers to scales higher up the stem, showing a 
transition to the structure of the foliage-leaf. 
Below the superficial rhizoid-bearing layer are two or three 
layers of living cortical parenchyma, thin-walled and polygonal 
in transverse section. This tissue is interrupted opposite the 
three ridges by the sclerenchymatous cells of the three hypo- 
dermal strands. The extent to which these strands are 
developed varies very much in different rhizomes, and in 
different parts of the same rhizome. They are usually quite 
massive (as in Bastit’s Fig. 41), and their cells have very thick 
and strongly lignified walls. In other cases their develop- 
ment is much feebler, the walls of their cells being only 
slightly thicker and darker than those of the ordinary cortical 
^.cells. The cells of the hypodermal strand are distinctly 
prosenchymatous, with pointed ends. They are living cells 
sometimes containing starch. 
As we pass radially inwards from the thick-walled hypo- 
dermal strand, we come to cells of greater diameter, and with 
