32 Tans ley and Chick. — Notes on the 
stances into the stem, and frequently hydroids associated 
with these. The leaf-bundles are not usually continued into 
the stem, the conduction in the stem itself of the formed 
substances coming from the leaves being carried on no doubt 
by the longitudinally elongated cortical cells. With regard 
to the conduction of water, it seems to take place, in some 
cases at least, across the cortex from the central strand to 
the bases of the leaves. But no doubt nearly all Mosses take 
up water through their leaves on occasion, while the aquatic, 
semiaquatic, and xerophilous types, as Haberlandt has shown, 
habitually do so, and possess no conducting system at all or 
one which is very feebly developed. It is probably owing 
to the retention of this primitive habit in many terrestrial 
Mosses that a more efficient water-conducting system is dis- 
pensed with. A certain number of terrestrial forms, however, 
have evidently felt the need of such a system. In Mnium , 
Bryum , and some species of Splachnum , the hydroids of the 
leaf-bundles are prolonged into the stem, but curiously 
enough, instead of crossing the cortex to join the central 
cylinder, they bend down and pursue a vertical course near 
the edge of the cortex, parallel with the long axis of the 
stem. These leaf-traces or their lower ends have their surface 
increased in various ways, i. e. they may be band-shaped 
or star-shaped in cross-section so as to present a larger surface 
to the cortical cells through which their water must come. 
In Funaria hygrometrica the leaf- traces take an obliquely 
radial course through the cortex, and approach the central 
cylinder, but usually just stop short of it, though in some 
cases they actually join it. Finally, in some species of 
Splachnum , in Voitia nivalis , and throughout the Polytri- 
chaceae, the traces regularly join the cylinder. 
The first thing that strikes one in considering this series 
of facts is the entire separateness in evolution between the 
primitive moss-stele and the leaf-bundles. Not only do they 
appear quite independently in the lowest types, but in the 
case of the (no doubt phylogenetically subsequent) continuation 
of the leaf-bundle back into the stem as a leaf-trace, the latter 
