182 
W. Watson. 
Stokesii, are at most semi-xerophytic, whilst Dicranella squarrosa, 
Paludella squarrosa , Hypnum stellatum, and H. riparium are usually 
found in wet situations. 
The xerophytic squarrose-leaved plants, however, have the 
peculiarity that the leaves, during drying, change their positions by 
curling, whereas in the other cases little alteration occurs. The 
squarrose leaf will certainly absorb water quickly, and in some cases 
the recurved apices have little chlorophyll, and form the external 
portions of the shoots (e.g., H. squarrosum). Grebe (8) states that 
the squarrose leaves of acrocarpous mosses have a similar structure 
to that of the curly mosses, having large, hyaline, extended cells 
below, and a close-meshed tissue above, but constantly have a 
broader lamina and a different structure of the midrib. 
( g) The Falcate and Secund Leaves of many Dicranaceae and 
Hypnaceae alter little during different states of humidity, but their 
importance often seems to be connected with protection from 
dryness, since one leaf forms a kind of protective hood to that 
beneath it, and at the same time a number of small water-reservoirs 
are formed. Falcate leaves are those in which the leaf is sickle¬ 
shaped ; secundity is said to occur when the upper portion of the 
leaf is oblique to its insertion on the stem. Neckera complanata in 
a dry state often has the tips of the shoots falcate, and when N. 
crispa grows on dry limestone this is the usual state and is the 
so-called variety falcata. Falcation and secundity are often 
associated, as in the xerophytic Dicranum spp. and in forms of 
Dicranella heteromalla. The falcato-secund character of the leaves 
is very pronounced in Hypnum molluscum (Fig. 3, 13) when it is 
growing on dry limestone, as well as in dry-habitat forms of 
H. cupressiforme and H. uncinatum , though no definite relation 
can be established between the degree of falcato-secundity and the 
nature of the habitat. 
The presence of secundity and falcation in many water plants 
prevents us from regarding it as primarily connected with xero- 
phily, though many of these plants grow in boggy localities, or in 
places where the water is liable to be dried up, e.g., Hypnum 
lycopodioides in fairly shallow pools of sand-dunes, H. jluitans and 
H. exanmdatutn in moorland pools, H. riparium v. subsecundum in 
drier places than where the type grows (23). 
Some liverworts also exhibit these characteristics, though in a 
slighter degree, e.g., some species of Sphenolobus, Herberta, Adelan- 
thus and Pleurozia , 
