146 CLASSIFICATION OF [CH. 



Glycena aquatica and G. fluitans are sweet grasses of value in 

 water-meadows only. The " seed " is not often met with. 



Not only with the Poas, but also with Catahrosa are there 

 difficulties in determination. Molinia and Koeleria also present 

 difficulties with Glyceria : the former has fewer and feebler nerves. 

 DigraphU and Arundo are easily distinguished by the basal hairs. 



= = Palea acute and somev:hat compressed and 

 keeled^ and %dth hairs on the ribs. Tips 

 nerved. 



Poa annua. 

 P. maritima. 

 P. distans. 

 P. rigida. 

 P. loliacea. 

 P. bulbosa. 

 P. alpina. 



Their "seeds" are all small, about 2 — 3'5mm. only, and angular, 

 brown, and present many difficulties (see note, p. 141). 



Poa annua, L. (Fig. 43). 



Palea 3*5 and caryopsis 2 mm. long, so that the " seed " 

 is much larger than P. trivialis, and there is no web. 

 Minutely silky-hairy on the keel, and the ribs are strong 

 for a Poa, 



Poa alpina, L., has the palea five-ribbed with stiffish 

 hairs below, but no web. Bronzy green-violet. " Seed " 

 3 — 3-5 mm. long. Caryopsis 1*5 — 2 mm., and slightly 

 grooved. It is rare in England, and is interesting as 

 it becomes viviparous in Alpine situations. 



(2) Apex of palea distinctly pointed, acuminate 

 or mncronate, but not giving rise to a true, 

 long, hristle-like awn. 



