The Natural History of British Grasses. 165 



— which may be long or short — bristly or doivny, in proportion as 

 this kind of armature may be coarse or harsh, ox fine and soft. 



The nodes again may be of a different colour from the culm, 

 or, like it, may be smooth or armed in a similar manner. 



The leaves (D) consist of the following parts : — 



D. The sheatli, = petiole, or leaf-stalk of other plants. 



D". The ligule, or tongue. 



D'". The lamina, = blade, or flat part of the leaf. 



The sheath is the footstalk of the leaf. This takes its rise from 

 the nodes, one from each, arranged on alternate sides of the culm. 

 The whole length of the sheath, which is variable, is folded 

 around the culm, from which it can be loosened by unwinding 

 without fracture, a circumstance which serves to distinguish the 

 grasses from the sedges [Carex), as the sheath of the latter is a 

 continuous tube, in which the solid and often triangular culm 

 is inserted, not folded. This is a distinctive character of great 

 importance to observe, inasmuch as grasses and sedges are out- 

 wardly much alike — indeed some species of the latter are called 

 Cai-nation Grass — but greatly different in quality ; grasses being 

 for the most part highly nutritious plants, whilst sedges are not 

 only usually innutritions, but, from the harshness of their herbage, 

 are often a source of injury and annoyance to the creatures that 

 from starvation are sometimes doomed to eat of them. 



The blade — lamina — D", is the expanded part of the leaf. It 

 is sometimes large and drooping, as in the larger or flag-like 

 grasses, but occasionally it is very minute, especially when com- 

 pared with the sheath, as in the Avena pubescens (soft oat-grass). 

 In some species the blade is long and the sheath short. The 

 blade is traversed by longitudinal parallel lines, which are called 

 the leaf-veins or nervures : these may be broad, narrow, riyid, soft, 

 armed with rough hairs, and so on, all of which are not only points 

 of distinction in species, but aid in making up the sum of those 

 differences which will ever be found in good and bad pasture 

 grasses : as, for instance, grasses in which the herbage is covered 

 with long downy hairs are mostly poor and innutritions in quality ; 

 on the other hand those of a harsh and rigid structure, with ser- 

 rated leaves, whose edges act as a saw and whose flat blades 

 perform the office of a file, even if nutritious, would nevertheless 

 be refused by cattle on account of their mechanical inconvenience. 



The ligule, I)'. — At the point where the sheath ends and the 

 blade begins occui's a thin and usually white semi-transparent 

 meml)ratie, termed the liyulc, or tongue. This, as it varies so 

 much in size and form, will be frcc{uently referred to in diagnosis 

 by some such terms as the following : — 



Short, in Poa pratensis, smooth-stalked meadow-grass. 



Pointed, in Poa trivialis, rougl.'-stalked ditto. 



