Acrogynous Jlingermanniales. 275 
there are two wings and the leaf is H-shaped in cross-section. In 
several genera, belonging to different families, we find paraphylls — 
leaf-like or filamentous outgrowths arising from the stem between, 
and in addition to, the ordinary leaves; in the curious genus 
Stephaiiiella, the leaves soon lose their chlorophyll and then serve 
as transparent scales covering the dense mantle of green filamentous 
paraphylls with which the stem is clad. Perhaps the most beautiful 
of these modifications, however, are the water-sacs or pitchers, 
formed by the infolding of either the entire leaf, or the large upper 
Fig. 48. Polyotus mugellanicus. Part of a plant showing lower surface of 
four of the ultimate branches, with numerous water sacs. 
lobe, or, more commonly, the small ventral lobe. Sometimes the 
pitchers are provided with a valve or trap-door like that of the 
Bladdenvort pitcher. The small ventral-lobe pitchers of Frullania 
(Figs. 46, 47) are well known, but similar pitchers occur in various 
genera belonging to different families, and in Polyotus (Fig. 48) we 
get a profusion of pitchers developed not only on the side-leaves 
but also on the underleaves. 
