OH. vi] Key to Grass "Seeds" 47 



Poa trivialis (p. 129), O.P. average 2-3 mm. long, 

 5-nerved, with acute apex ; the "seed" 

 is acutely triangular in transverse 

 section, and without hairs on the 

 marginal ribs; rachilla smooth and 

 slender. (Fig. 143.) 



Poa pratensis (p. 127), O.P. average 2-2 mm. long, 

 with blunt apex; "seed" stouter, and 

 less acutely triangular in transverse 

 section than P. trivialis', a few hairs 

 are frequently present on the marginal 

 ribs below; rachilla smooth. (Fig. 142.) 



Poa compressa, very similar in size, etc., to P. pralensis 

 but there are no intermediate nerves 

 between the keel and marginal ribs of 

 the O.P., and the I. P. is fringed with 

 finer and more numerous microscopic 

 hairs. (Fig. 138, p. 124.) 



N.B. "Seeds" of the above four species in their natural 

 state have a "web" at the base; 

 "seeds" of the two following species 

 have no "web." 



Poa annua, O.P. from 2-3 mm. long, 5-nerved, with 

 membranous edges above; keel and 

 lateral ribs fringed with hairs. Ra- 

 chilla relatively large. The degree of 

 hairiness is very variable. (Fig. 136.) 



Poa alpina, O.P. 3-4 mm. long, 3-nerved, acutely 

 pointed and keeled; keel and lateral 

 nerves are covered with long white 

 hairs. (Fig. 135.) 



2. "Seed" with O.P. round-backed, i.e. without a promi- 

 nent keel. 



(a) O.P. not inflated, closely investing the grain. 

 Phleum pratense (p. 121), "seed" about 1-8 mm. 

 long, spherical-ovoid in form. Paleae 

 silvery- white ; grain yellow with ir- 

 regularly pitted surface. (Fig. 134.) 



