Xerophytic Adaptations of Bryophytes. 16x 
or disappear entirely, and all these plants are found in moister or 
shadier situations than their types. On the other hand the grey 
tint due to the hairs is shown by drier ground forms of some mosses, 
in which the apical hyaline cells are not usually pronounced, e.g., 
Phascumcuspidatumv.piliferum,Pottia bryoides form pilifera, Tortilla 
pusilla v. incana. Bryum argenteum when growing in very sunny 
situations has a longer point (var. lanatum), but when in damper 
places, its leaves are chlorophyllous almost to the apex (var. majus). 
Hedwigia ciliata also has two habitat-varieties, the hoary leucophcea 
of exposed positions, and the greener viridis of more shaded 
localities. In genera which usually possess these hairs, the more 
or less aquatic species are devoid of them (e.g., Rhacomitrium 
aciculare, R. protensuin, Grimmia atrata, Tortilla inutica), no water- 
plant has them, and they are usually absent in those mosses which 
are otherwise sufficiently provided for xerophytically, as in those 
with curly leaves (e.g., Trichostomum, Weisia). 
Few liverworts possess hairs, but they are found on the thalli 
of Metzgeria and Riccia, especially in the dry ground forms. 
Amongst the foliose liverworts, the leaves of Mastigophora and 
Ptilidium (Fig. 2, 6) are ciliate, and both these plants grow in dry 
spots, or in places which are liable to desiccation. In Ptilidium the 
species of drier ground ( P . pulcherrimum) has the longer cilia, the 
plant of wet places (P. ciliare v. inundatum) having fewer and 
shorter ones. 
(b) Long-pointed Leaves, with few chloroplasts in the apical 
cells act similarly to the hair-pointed leaves. The following xero- 
philous mosses have long-pointed leaves :— Seligeria Doniana, 
Dicranella secunda, Dicranum falcatum, D. fuscescens, D. strictum, 
D. montanum , D. uncinatum, D. asperulum, D. longifolium, Ortho- 
dontium gracile, Neckera pumila v. Philippeana, B r achy the cium 
glareosum, Ditrichum flexicaule, etc. In Hylocomium squarrosum and 
to a less extent in H. loreum, the fine and paler tips of the squarrose- 
recurved leaves form the external portions of the shoots. Some 
liverworts display a similar principle in the lengthening of the leaf- 
lobes, e.g., Lophocolea cuspidata (Fig. 2, 5). 
(c) Ventral Scales of Marchantiales. During dryness the thallus 
of species of Pressia, Reboulia, Targionia, Riccia, etc., curves round 
so as to expose the non-chlorophyllous or slightly chlorophyllous 
ventral scales, which are often of a purplish colour. These scales 
cover over the incurved thallus, the chlorophyllous cells of which 
are not only protected by one or two layers of empty epidermal 
cells, but also by the scales as well, 
