ABSORPTION OF WATER BY LICHENS AND MOSSES. 219 
leaflets. In many instances this felt of rhizoids does not come into contact at all 
with the soil, rock, or bark (as the case may be), but is surrounded by air alone, 
and is able to condense or attract, to use a common expression, the aqueous vapour 
of the air like a piece of cloth or blotting-paper. In dry weather, it is true, mosses, 
like lichens, lose their water, but they part with it much more slowly than the 
latter. This is chiefly due to the fact that the moss-leaflets at the commencement 
of a drought wrinkle, curl up, become concave, and lay themselves one above the 
other, so that the water is retained at the bottom for a longer period. 
A very remarkable contrivance for the absorption of water from the atmos- 
phere is also exhibited by the white-leaved Fork-mosses (Leucobrywm) and Bog- 
mosses (Sphagnacez). Although they possess chlorophyll, and assimilate under the 
Fig. 49.—Porous Cells. 
10f the white-leaved Fork-moss (Leucobryum); x550. 2 Of the Bog-moss (Sphagnum); x230. 3Of the root of an Orchid 
(Lelia gracilis); x310. 
influence of sunlight, yet they look like parasitic and saprophytic plants destitute 
of chlorophyll. They are of a whitish colour and always grow in great cushion- 
like sods, so that the spots where they grow are deficient in verdure, and stand 
out conspicuously from their surroundings in consequence of their pale tint. 
Microscopie investigation at once explains this appearance. The cells containing 
chlorophyll and living active protoplasts are relatively small, and, as it were, 
wedged and hidden between other cells many times as great, which have entirely 
lost their protoplasm by the time they are mature, and then cause the paleness of 
colour appertaining to the plant as a whole. The walls of these large colourless cells 
are very thin, and in the Bog-mosses have spiral thickening-bands running round 
them, being thus secured against collapse. After remaining for a time in a dry 
environment they are full of air only; but the moment they are moistened they 
fill with water. If there were an actively absorbent protoplast at work in the 
interior, the water would be able to pass into the cell-cavity through this easily 
moistened wall, as in the case of other mosses, owing to the delicacy of the cell- 
membrane. But the air which fills the cells is not absorptive, and in the case of 
Leucobrywm and Bog-mosses the water reaches the interior, not in consequence of 
