GRASSES OF SCOTLAND. 75 



itiuralis, a slender variet\-, from five to eight inches 



high, with a short, upright panicle. Frequent on tops of walls in 

 shady places. (Plate XXXIV. ) 



arenaria, a stout upright variety, ^"ith large, somewhat 



angular spikelets. Outer palea seven-ribbed. Inner palea fre- 

 quently di^■ided to the base. The whole plant somewhat of a glau- 

 cous appearance. Frequent in sandy situations along the sea coast. 

 (Plate XXXIV.) 



Many other varieties might be enumerated assuming various forms, 

 but those already noticed will be sufficient to show, that, whatever 

 the variety may be, whether of a most luxm-iant habit, or of a small 

 stunted growth, the specific characters always remain constant, name- 

 ly, upper leaf much shorter than its sheath ; the li^ule obtuse ijiorets 

 webbed ; outer palea five-ribbed, (except in variety arenaria), with the 

 marginal ribs hain", so that Poa pratensis can never be confounded 

 with any other Poa. ' (See Figs. 1 and 2, which represent the calvx 

 and floret magnified ; Fig. 5, the obtuse ligule. ) 



Obs. — Poa pratensis is distinguished from Poa frivialis in the ligule 

 being obtuse, and the marginal ribs of the outer palea hairy : — whereas 

 in P. trivialis the /;^«/^ is long and pointed, and the marginal ribs of the 

 outer palea are not in the slightest degree hairy.* (See Fis. 4.) 



From Poa nemoralis, in the i/pper sheath being much longer than 

 its leaf ; ligule prominent : — whereas in P. nemoralis the upper 

 sheath is about equal in length to its leaf, and sometimes even 

 shorter ; ligule very short, scarcely perceptible. (See Plate XXX VL 

 Fig. 5.) 



From Poa compressa, in the upper sheath being much longer than 

 its leaf : outer palea five-ribbed ; — whereas in P. compressa, the up- 

 per sheath is about equal in length to its leaf ; outer palea only three- 

 ribbed. (See Plate XXX Vn. Fig. 4.) 



It is distinguished from all other British grasses in the lower florets 

 beinsj webbed. 



• The roughness or smoothness of the sheaths is supposed br some authors to form a 

 good specific character, but it cannot at all times be depended on, as in some varieties of 

 P. pratcn-Tii the sheaths are occasionally roughish, while in P. triTiali4 thev are 

 times ncarlv smooth. 



