106 A TEXT-BOOK OF GRASSES 



grass leaf at the junction of the sheath and blade. The 

 usual form of the ligule is a membrane extending across 

 the top of the sheath at first tightly clasping the culm, the 

 membrane being longest in the middle portion. The shape 

 and appearance of the ligule are characteristic of each 

 species and are often used for taxonomic purposes. 



The ligule may be truncate or even somewhat concave on the 

 upper margin. It is nerveless but may be 1-keeled (Dactylis glom- 

 erata) or apparently 2-keeled by the extension upward of the base 

 of the blade on each side. Not infrequently the ligular tissue extends 

 down the margins of the sheath. Sometimes the ligule is lacerate or 

 ciliate, or may appear as a row of hairs (Panicum Lindheimeri Nash 

 and its alhes) . The ligule is obsolete in some species {Panicum sphsero- 

 carpon Ell.) and entirely absent in others (Echinochloa crus- 

 galli (L.) Beauv.) In Anthochloa colusana (Davy) Scribn. there is 

 no differentiation into sheath and blade, hence no collar or ligule. 

 The exact morphology of these leaves has not been investigated. It 

 may be the sheath that is obsolete. 



136. The blade is the usually flat part of the leaf 

 beyond the sheath and is the chief foliage organ of the 

 plant. In most grasses the blade is many times longer 

 than wide but in many tropical species and in a few of the 

 temperate regions it is short and broad, from oval to 

 lanceolate in outline (see Fig. 29). Grasses with this kind 

 of blade are mostly confined to the damp forest regions 

 of the tropics. 



In such grasses the shoots are often strongly dorsiventral, the 

 blades being turned into the plane of the culm, and the shoots 

 usually prostrate, procumbent or ascending. The genera Oplismenus, 

 Ichnanthus, Senites, Pharus and many species of Panicum (as P. 

 trichoides) furnish familiar examples of species with broad short 

 blades that are found on the floor of tropical forests. These blades 

 often resemble those of other families of plants, especially Commely- 

 naceae. The bamboos and the bamboo-panicums (Lasiacis) usually 



