﻿GRASSES OF SCOTLAND. 89 



palea of lowermost floret five-ribbed (Fig. 4); the lower half of 

 the dorsal as well as the marginal ribs hairy ; the intermediate ribs 

 naked and rather indistinct. Inner palea nearly as long as the outer 

 palea, with two green marginal ribs minutely fringed. The whole 

 plant is more or less glaucous. 



Obs. — Poa ccesia somewhat resembles Poa alpina, but differs from 

 it in the upper sheath being about equal in length to its leaf. Ligule 

 obtuse, and the outer palea five-ribbed ; — whereas in P. alpina the 

 upper sheath is much longer than its leaf. Ligule long and pointed, 

 and the outer palea three-ribbed. (See Plate XXXVII.) 



From Poa polynoda, in the stem bearing but two joints ; upper- 

 most joint situated near the root, leaving two-thirds of the stem nak- 

 ed ; second sheath covering the first joint, and the lowermost floret 

 projecting beyond the large glume of the calyx ; — whereas in P. poly- 

 noda the stem has six or more joints ; upper joint near the panicle; the 

 second sheath not reaching to the first joint ; and the summit of lower- 

 most floret not projecting beyond the calyx. (See Plate XXXIX.) 



From Poa laxa, in the upper sheath being about equal in length to 

 its leaf; ligule obtuse ; and the outer palea five-ribbed ; — whereas in 

 P. laxa the upper sheath is much longer than its leaf; ligule long and 

 pointed; and the outer palea three-ribbed. (See Plate XXXVIII.) 



From Poa montana, in the uppermost joint being situated near the 

 base of the stem ; root fibrous, and the summit of the lower floret pro- 

 jecting beyond the large glume of the calyx ; — whereas in P. montana 

 the upper joint is situated about the centre of the stem ; the root is 

 extensively creeping ; and the summit of the lower floret does not pro- 

 ject beyond the calyx. (See Plate XXXIX.) 



Among the Poas which are webbed, Poa casia is distinguished 

 from Poa nemoralis, in the florets not being webbed ; upper joint being 

 near the base of the stem ; and the second sheath extending beyond 

 the first joint ; — whereas in P. nemoralis the lowermost florets are dis- 

 tinctly webbed, suspending the calyx ; uppermost joint placed about 

 the centre of the stem ; and the second sheath does not extend to the 

 first joint. (See Plate XXXVI.) 



From Poa compressa, in the florets not being webbed, and the outer 

 palea five-ribbed ; — whereas in P. compressa the lower florets are 



