Conducting Tissue-System in Bryophyta . 9 
little or none. The midrib, in the not very strong specimens 
examined, was ten to twelve cells thick. Approximately in the 
centre of the rib, but rather nearer the dorsal surface, is a strand 
of narrow thick-walled cells, about twenty in the specimen 
here described (considerably more in the one represented in 
Fig. 3), the whole of the strand being about the width of 
a single large cell in the cortex of the rib. The thick walls 
of these cells are greyish in thin, and yellowish in fairly 
thick transverse sections. They appear perfectly homo- 
geneous. In longitudinal section (Fig. 4) they are seen to be 
considerably elongated, and pointed at the ends, their walls 
being covered with small pits arranged on a spiral, making 
quite a small angle with the horizon. The pits are sometimes 
circular, but more often elongated, sometimes considerably, 
in the direction of the spiral. They are rather irregularly 
scattered over the walls, considerable areas being destitute 
of them. In sectional view they are seen to be perfectly 
normal simple pits. A inch oil immersion is needed for 
a clear view of their structure. Where a strand-cell abuts on a 
cortical cell the thinner wall of the cortical cell is seen to 
be quite without pits, but the adjacent wall of the strand-cell 
may be richly pitted (Fig. 4). 
Here and there in the strand-cells, a little contents can be 
seen, which are no doubt the remains of protoplasm. All 
stages of the disorganization of this can be seen in longitudinal 
sections close to the apex. The strand-cells are formed, as 
might be expected, by longitudinal division of the inner cells 
cut off from the segment of the apical cell. They are differen- 
tiated very close to the apex. 
A few experiments were made to find out whether the strand 
actually conducted water. A piece of the thallus was cut off, 
and its cut , end dipped into watery eosin, to a depth of 
about 3 mm. After a certain time the lower part of the 
strand became visible through the cortical tissue of the midrib 
as a red thread. In one case it could be seen 1 cm. above 
the level of the solution in the course of 20 minutes, on a hot, 
sunny day ; in another, on a grey, damper day, the same 
