158 W. Watsoii. 
Many of the bryophytes exhibiting xerophytic devices are 
mountain or alpine plants (some of the Andreceas and Grimmias 
being found in the highest regions), but they are not limited to any 
altitude, seeing that they are present even at sea level, in fact, 
many of the plants growing on sand near the sea are essentially 
xerophytic, owing to the water derived from the substratum having 
a high osmotic value due to the large amount of dissolved salts. 
Two general methods are adopted (A) the output of water is 
reduced, and this is the commoner method, or (B) some method of 
storing water is provided. Sometimes the same apparatus serves 
for both methods and will be considered under the first. As special 
protective devices the following may be given :— 
A. REDUCTION OF WATER-OUTPUT. 
(1) Cushion-forming Habit. 
Many bryophytes grow in cushions or tufts, these being 
especially definite in such plants as Grimmia pulvinata and Ulota 
crispa. The interspaces between the leaves are markedly shortened, 
and the branches, when present, are closely crowded together. The 
cushion is capable of quickly absorbing water, and of retaining it 
for a much longer time than the free plant would be able to do, as 
only the apices of the leaves are exposed to evaporation. Everyone 
who is familiar with the tufted vascular plants knows how this 
character is increased in areas exposed to the wind, and the same 
thing is also true of these smaller plants. Under shadier, less 
exposed or damper conditions, the tufts are looser and higher, but 
when growing on exposed rocks or trees, they become compacter, 
so that not only is evaporation reduced, but they become more 
stable, since they offer a less area to be acted upon by the force of 
the wind. 
Amongst tufted mosses growing on rocks, Grimmia pulvinata , 
G. anodon, Trichostomum crispulum, T. nitidum , Orthotrichum 
anomalum , Eucalypta vulgaris , Tortula muralis , T. ruralis, Barhula 
convoluta, B. revoluta, offer excellent examples, the liverworts being 
represented by Gymnomitrium obtusum , G. coralloides, G. alpinum, 
Sphenolobus saxicolus, Cololejeunea calcarea, etc. 
As tree representatives of this group may be mentioned 
Zygodon viridissimus, Ulota crispa , and Dicranum montanum. 
Many mesophytic or hydrophytic plants have a form or variety 
of drier habitat which adopts this compact habit, enabling it to live 
in its drier position, e.g., Ditrichum jlexicaule var. densum, Bryum 
