VEGETATIVE ORGANS OF GRASSES 345 



LEAVES. 



"The leaf is a lateral organ of the stem, borne singly at the 

 nodes "^*'. The two conspicuous parts of the leaf are the sheath 

 and the blade. The sheath or leaf base enwraps the stem and 

 opens on the side oppoisite the leaf and is cylindrical in form. 

 The color of the sheath is usually light green to white at the 

 base but in some species it is distinctly colored. The blade forms 

 the chief foliage organ and is usually flat, sometimes depressed 

 in the middle along the midnerve. The ligule is formed at the 

 top of the sheath at the junction of the blade and sheath. The 

 ligule is membranous, seemingly a continuation of the lining of 

 the sheath. The ligule is a significant character in the identifi- 

 cation of young grasses. In some cases the ligule is absent, but 

 when present it may be .classed as to form ; these forms are de- 

 scribed, according to Carrier^^ "as entire, when there are no 

 notches or indentations along the margin, lacerates, 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 with hairs. '•' The iden- 

 tification of the ligule is more difficult after the grass becomes 

 older as the ligule becomes split and sometimes an entire ligule 

 of a young shoot will appear ciliate when it becomes older. The 

 collar when present is distinguished usually by a lighter col- 

 ored band, or by a difference in texture at the junction of the 

 sheath and leaf. It is scarcely distinguishable in some species, 

 and in others it is a marked character. In some instances it is 

 pubescent. It may be a continuous band extending across the 

 leaf, arising at the base of the ligule and extending upward 

 about 2 to 3 mm. In some species it is wider on either margin, 

 in others it is completely divided into two parts by the mid- 

 nerve. The auricles are membranous appendages projecting 

 from the collar or from the top of the sheath. 



The vascular system is represented in the grasses by nerves 

 of the culm, midnerves of the leaif and nerves of the siheath which 

 are continued in the leaf. They are very conspicuous in some 

 species, as in Agrostis alba, and in others are scarcely discernible. 



"Hitchcock, A. S., A Text Book of Grasses, p. 103. 



"Carrier, Lyman, Identification of Grasses by Tlieir Vegetative Cliaracters : 

 U. S. Dept. Agric. Bull. 461, 1917. 



