IDENTIFICATION OP GRASSES. 3 



Leaves (fig. 3). — A grass leaf consists of two principal parts, the 

 sheath or tubular basal portion which incloses the stem, and the 

 blade, nearly always long, narrow, and most commonly flat. The 

 sheaths are usually cylindrical in form, but in some grasses they are 

 laterally compressed, forming a keel at the back, in which case they 

 are described as compressed. In some grasses the nerves of the 

 sheaths are prominent, in others scarcely noticeable. A few grasses 

 have distinctively colored sheaths, the coloration being especially 

 noticeable in the portion below ground. At the junction of the 

 sheath and the blade are structures that are very useful in identify- 

 ing grasses not in blossom. On the inside of the sheath is a small 



Fig. 1. — A common sedge. 



Fig. 2. — A Juncus. 



Fig. 3. — Different parts of a 

 grass : A, Blade ; B, ligule ; 

 C, collar ; D, sheath ; E, 

 shoot or bud leaf. 



organ, the ligule, apparently a continuation of the lining of the 

 sheath and usually very thin in texture. It usually consists of a thin, 

 semitransparent membrane, but sometimes it is a mere fringe of 

 hairs, and only in rare cases is it wholly absent. The ligules of some 

 grasses are wider than the sheaths and continuous with the hyaline 

 margins. Owing to its wide variation in form, the ligule is one of 

 the most dependable of characters for identification. Several special 

 terms are necessary to describe these forms : Entire, when there are 

 no notches or indentations along the margin; lacerate, when the 

 margin is much cut ; truncate, when the apex is apparently cut off 

 squarely; acute, when the apex terminates in a sharp point; and 

 ciliate, when the margin is fringed wit^h hairs. Other terms, such 

 as " toothed along the margins," or " hairy on the back," are self- 

 explanatory. 



