164 
W. Watson. 
E. myurum, Sphenolobus minutus, Lophozia bicrenata, L. confertifolia, 
Ceplialozia bicuspidata v. conferta, and in the alpine E. cirrosum, 
S. saxicolus, Pleuroclada albescens, Marsupella condensata, M. apiculata, 
Gymuomitrium spp., and Odontoschisma Macounii. 
(e ) Undulate Leaves. The reduction of the transpiring surface 
is accomplished by the lamina being transversely folded, thus 
forming a number of small chambers in which the water can be 
retained. They are beautifully shown in species of Neckera (Fig. 3, 9), 
as well as in Dicranum undulatum, D. spuriuni, and Plagiothecium 
undulatum. On dry heaths Hylocomium triquetrum, H. splendens, 
Dicranum scoparium and some other non-undulate species of mosses, 
are often found with undulate leaves. In H. rugosum and Dicranum 
Bonjeani v. rugifolium the small chambers are more of the nature 
of little pockets than transverse folds. The wavy nature of some 
liverworts has a similar purpose, e.g., Petalophyllum Ralfsii, Alien- 
laria Geoscyphus, Lophozia incisa, and dry ground forms of L. Floerkii. 
(/) Plicate Leaves, in which the folds are arranged longitudinally 
may serve for strengthening purposes, but the main use of the 
plication seems to be for protection against dryness. This form of 
leaf is found in Camptotliecium sericeum (Fig. 3, 8), C. lutescens, 
Leucodon sciuroides, Brachythecium plicatum,B. albicans, Eurynchium 
strigosum, E. striatum, Ptychomitrium polyphyllum, Breictelia arcuata, 
and species of Thuidium and Hylocomium. It is commoner amongst 
the pleurocarpous than the acrocarpous mosses, and as Grebe (8) notes, 
mosses with plicate or undulate leaves have few other protective 
arrangements, the cells are poor in chlorophyll, and the cell- 
membranes are firm and tough. Plicae are present in some 
apparent hydrophytes as Hypnum uncinatum and Climacium den- 
droides, but even these are able to suffer dryness, as I have found 
them in such dry places as on Carboniferous Limestone heathy 
pasture. It is also to be noted that some forms or varieties of such 
plants, growing in water poor in osmotic substances, have the leaves 
less plicate than the type, e.g., vars. falcatum and virescens of 
Hypnum falcatum. 
4. The Size of the Leaf-cells. 
The cells are usually smaller in xerophytic bryophytes, but not 
always so, since other adaptive characters must be taken into 
account; it is, however, the rule in comparing two or more species 
of the same genus, to find the smaller-celled one to be a plant of 
drier habitat. The large-celled mosses, Pterygophyllum lucens 
