2 BULLETIN 461, U. S. DEPARTMENT OF AGRICULTURE. 



grasses. Lewton-Brain x has described the leaf anatomy of many 

 British grasses. 



The general plan of classification used in this bulletin follows some- 

 what that of Percival, but it is enlarged to include about three times 

 the number of grasses described by him. 



WHAT IS MEANT BY THE TERM " GRASS." 



In this discussion the term " grass " is restricted entirely to those 

 plants which botanists group in the family Graminese or Poaceae 

 and does not include the clovers and some other forage plants which 

 are often classed agriculturally under the term "grass." The true 

 grasses are recognizable by the following characters: Stems jointed, 

 usually hollow ; leaves in two ranks on opposite sides of the stem, 

 each consisting of two parts, the blade 7 usually narrow and elon- 

 gated, and the sheath, or basal portion, tubular and enwrapping 

 the stem, its margins free or rarely grown together; leaf nerves 

 parallel ; at the junction of the sheath and blade a small membranous 

 appendage, the ligule, which is sometimes wanting. 



The plants which are most likely to be mistaken for grasses are the 

 sedges (fig. 1), characterized by 3-ranked leaves on a solid, usually 

 3-angled stem, and the rushes (fig. 2), distinguished by solid stems, 

 tubelike closed sheaths, and cylindrical or straplike leaves, neither 

 folded nor rolled in the bud, and without ligules. 



CHARACTERISTICS OF GRASSES BEFORE THE BLOOMING STAGE. 



Grasses, like other flowering plants, may be considered as made up 

 of roots, stems, leaves, and flowering parts. The natural classifica- 

 tion of grasses is based mainly on the flowers and fruits, but the other 

 organs show much variation in structure ; indeed, sufficient to identify 

 most grasses from their vegetative parts alone. 



Roots. — The true roots of grasses are very slender and often much 

 branched. The}' vary less than other organs, however, so that it is 

 rarely possible to identify a grass from its roots alone, at least from 

 the gross structure. 



Stems. — Apart from the erect stems of grasses, which are usually 

 flower bearing, many species have stems of a different sort. In some 

 cases these are creeping, leaf bearing, and often rooting at the joints. 

 Such steins are termed stolons. Many grasses have underground 

 stems. These are jointed, bear scalelike reduced leaf sheaths, and are 

 usually horizontal and coarser than roots. Such underground stems 

 are termed rootstocks or rhizomes. 



1 Lewton-Brain, Lawrence. On the anatomy of the leaves of British grasses. In Trans. 

 Linn. Soc, London, s. 2, Bot.. v. 6, pt. 7, p. 315-359, pi. 36-40. 1904. 



