34 Tans ley and Chick. — Notes on the 
a demand, and Haberlandt has shown that conduction of 
water up the central strand and its passage thence into the 
leaf-traces and leaf-bundles, to meet the losses caused by- 
transpiration, is a regular occurrence in Mnium undulatum. 
Finally, the more direct and efficient method of the establish- 
ment of continuity between the hydrom of the stem-cylinder 
and the hydrom of the leaf-bundle has been adopted in the 
case of other species of Splachnum , and in all the Polytricha- 
ceae. In the last-named family we have, for the first time, 
the ‘ Leitparenchym ’ (some of the cells of which have now 
assumed the characters of a distinct leptom) also continued 
down, side by side with the hydrom, from the leaf-bundle 
into the leaf-trace, and so into the leptom-mantle and starchy 
hydrom-sheath of the stem-cylinder. 
We think that the present theory is distinctly borne out 
in rather a striking way by the facts with regard to the 
constitution of the Polytrichaceous stem-cylinder set out at 
the end of the last section. The central thick-walled hydrom- 
cylinder is entirely independent of the leaf-traces and passes 
up to the top of the stem, wherein the case of a sporogonium- 
bearing shoot it changes its characters, becoming thin-walled 
and often mixed with cells having dense proteid contents and 
envelopes the base of the sporogonium. This, in our view, 
is the primitive hydrom-cylinder of the stem of the gameto- 
phyte. The thin-walled peripheral hydrom-mantle, on the 
other hand, composed, as Haberlandt has pointed out, of 
elements identical with the hydroids of the leaf-traces, is as 
a matter of fact entirely formed from the bases of the hydrom- 
strands of these traces, and decreases in thickness upwards, 
ceasing to exist above the level of exit of the last of the 
traces ; while below it rapidly diminishes after the lowest 
of the traces has joined the stele, and is represented in the 
rhizome by a very few elements in the region of the ‘ peri- 
cycle.’ The peripheral hydrom-mantle is then a new forma- 
tion, only arising with the attachment of the bases of the 
leaf-traces to the stem-cylinder. 
Nearly the same may be said of the leptom-mantle, which 
