F. Cavers. 
274 
Frullania), though sometimes the ventral lobe is the larger and the 
leaves succubous ( Diplophyllum , most species of Scapania). In 
some cases, the leaves are “fused” in pairs across the dorsal side 
of the stem ( e.g ., some species of Calypogeia) ; in others, the leaves 
are not only united dorsally but their lower margins are continuous 
with the sides of the underleaf that stands between each pair of 
leaves ( Arnellia, Southbvn) ; while in Syzygiella, which has no under¬ 
leaves, the leaves are joined both above and below, so that the stem 
appears to pass through a series of funnel-like double leaves. 
Fig. 47. Frullania dilatata. 
It is among the forms with folded leaves that we find some of 
the most remarkable examples of the plasticity of the Acrogynous 
leaf, mostly serving for the storage of water in various ways. In 
Mytilopsis, the leaf is so sharply folded that the two lobes lie almost 
parallel, like the valves of a mussel shell open anteriorly by a 
narrow slit, while the sharp keel bears a narrow wing. In 
Micro pterygium, Gottschea, etc., the leaf bears a conspicuous wing 
similar to that found in the Moss-genus Fissidens —in G. ciliata 
