146 CLASSIFICATION OF [CH. 
Glyceria 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 Catabrosa are there 
difficulties in determination. Molinia and Keleria also present 
difficulties with Glycerta: the former has fewer and feebler nerves. 
Digraphis and Arundo are easily distinguished by the basal hairs. 
== Palea acute and somewhat compressed and 
keeled, and with 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°5 mm. only, and angular, 
brown, and present many difficulties (see note, p. 141). 
Poa annua, L. (Fig. 48). 
Palea 3°5 and caryopsis 2mm. 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—35 mm. long. Caryopsis 15—2mm., 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 mucronate, but not gwing rise to a true, 
long, bristle-like awn. 
