Ill] VEGETATIVE CHARACTERS 45 



Poa pratensis presents similar difficulties to P. trivialis : for 

 diagnoses see p. 42. It is distinguished from P. nemoralis by its 

 closed sheath, thicker, blunter and harder leaves, linear-elliptical 

 shoot-sections, and light coloured nodes, as well as by its habit. All 

 other Poas have shallow and poorly developed roots. 



P. fertilis is a form very like P. nemoralis, with rougher lea\'es 

 and longer ligule, introduced into cultivation. 



** Margins of leaves scahei'idous with descending hairs. 

 Verif low fiat ridges. Sheath smooth. 



Briza media, L. (Quaking Grass). A weed in meadows, 

 indicating poor soil — e.g. moorlands and chalk — but eaten 

 by sheep. Tufted and slightly creeping perennial. Ligules 

 very short, entire. 



Briza minor, L. (Lesser Quaking-grass). Annual. 

 Leaves broader and shorter, and ligules longer. In the 

 south and rarer. 



11. Sheaths split, at least some distance down, 



A. Glabrous— i.e. with no obvious hairs ^ 



ill) Grasses with setaceous or bristle-like leaves ; — 

 i.e. the lamina of the lower leaves remains 

 permanently folded instead of opening out tlat. 



(1) Ligule obsolete, auricled at the junction of blade and 

 sheath. 



Festuca ovina (Sheep's Fescue). Densely tufted per- 

 ennial. Leaves hard, glabrous and often glaucous, with 

 5 — 7 ridges if forcibly unrolled, ears short, stitf and erect. 

 Branches in permanent sheaths. Chiefly useful as pastures 



1 They may have short microscopic asperities, but there are no 

 distinct long hairs. 



