40 CLASSIFICATION ACCORDING TO [CH. 



large air-cavities ; ligule short. Leaf-base with a brown 

 triangle. Margins and keel rather rough. 



These two species of Glycena are distinguished by their shoot- 

 sections and the ridges of the leaves of O. flwitans : they often occur 

 in the same ditch. 



They cannot readilj' be confused with others on account of their 

 aquatic habit, and the characters given. The only other aquatic or 

 semi-aquatic species are forms of Catabrosa, Digraphis, Arundo, 

 Alopecurus geniculatiis, Molinia ccei~alea and the rare Calamagrostis. 



The ligule and flat shoots with closed sheaths alone suffice to 

 distinguish it from the round and split sheathed Arundo Phrag- 

 mites ; and the round shoots of Digraphis, its split sheath and firm 

 leaves, suffice to distinguish it. 



Molinia also has a tuft of hairs instead of a ligule, and a split 

 sheath, and its habit is different. 



Alopecurus geniculatus, with its "kneed" shoots, has a totally 

 different habit from Glyceria, and its very high ridges and want of 

 visible air-chambers complete the diagnosis. 



Catabrosa is a small creeping aquatic with very flaccid leaves, 

 quite glabrous and soft. Also sweet-tasting. 



B. Not aquatic, and devoid of visible air-chambers in leaf 

 or sheath. Often perennial, i.e. having stolons or other 

 branches with no rudiments of flowers in them, and 

 with relics of old leaf-bases. 



(a) Sections of sheathed leaves acute : either two- 

 edged or four-edged. 



(1) Section of sheathed leaves quadrangular. Blades of 

 leaf thin and dry, sparsely hairy. Sheath quite 

 entire. Woods and shady places. 



Melica iiniflora, L. (Wood Melick). Lamina slightly 

 tapered below, convolute. Ligule obsolete, with a stiff 

 subulate process on the sheath opposite the blade- 

 insertion. Kidges below, but not above. 



