44 CLASSIFICATION ACCOEDING TO [CH. 



The Bromes are extremely variable and diflScult to determine by 

 the leaves. The annual species are apt to be biennial or {B. sterilis) 

 perennial ; and some vary much as regards hairiness — e.g. B. mollis 

 is connected by a series of semi -glabrous forms to varieties quite 

 smooth, all grouped by Bentham under B. arvends. 



Bromus asper, being auriculate and a shade-species, runs some 

 risk of confusion with Hordeum sylvaticum, but Hwdeum has a 

 split sheath and in B. asper the translucent interspace between the 

 ridges is 2 — 3 times as broad as in Hordeum sylvaticum. 



The other species of Bromus are not eared, and their entire 

 sheaths at once distingiiish them from Hordeum. 



Bromus giganteus has leaves glabrous and very like Festuca 

 elatior. The red split sheaths of the latter, its sharp ears and 

 prominent ridges afford the best distinctions ; and B. giganteus has 

 broader leaves and more evident serrulation or descending bristles 

 at the basal margins. 



(2) Section of sheathed leaves elliptical, owing to the 

 shoots being compressed. Sheaths often only slightly 

 split above. No hair on surface of leaves or sheaths. 



* Margins of leaves smooth and even. Blades without 

 ridges, a keel and flanking lines, acute, base rounded. 

 Ligule of lower leaves very short. 



Poa pratensis, L. (Smooth-stalked Meadow-grass). 

 An early and valuable dry pasture-grass, but though 

 deep-rooted, it yields thin hay: its chief value is for 

 "bottom grass" and in lawn mixtures, &c. Leaves stiff and 

 pointed. Extra-vaginal rooting underground stolons, and 

 intra-vaginal branches. Shoots smooth. Keel slight : seven 

 principal veins and smaller ones between. Leaves blunter 

 and broader than in P. trimalis. 



Poa alpina, L. (Alpine Poa). On mountains in the 

 north. No stolons. 4 — 5 veins on each side of the median 

 one. 



