6 



MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



they spread as impurities in the seed 

 of crop plants. That seeds may travel 

 great distances through the air has 

 been shown by experiments in which 

 airplanes have collected seeds, in- 

 sects, and other objects at varying 

 heights in the atmosphere. For ex- 

 ample, spikelets of Paspalum dila- 

 tation and P. urvillei were taken at 

 altitudes up to 5,000 feet in Louisiana. 



Grasses introduced into cultivation 

 may spread or "escape" from culti- 

 vation and become established over 

 wide areas. Kentucky bluegrass (Poa 

 pratensis) and the ryegrasses (Lolium 

 perenne and L. multiflorum) are 

 familiar examples. Johnson grass is 

 an excellent forage grass, but if it 

 escapes into cultivated fields may 

 become a troublesome weed. 



Other cultivated grasses, such as 

 the grains, frequently spread from 

 fields but are unable to maintain 

 themselves for long. Eulalia (Mis- 

 canthus sinensis) has been cultivated 

 for ornament in the eastern part of 

 the United States for many years. 

 Recently it has shown a tendency to 

 spread by seed. It is now becoming 

 a nuisance in some localities because 

 of its aggressiveness in old fields. 



MORPHOLOGY OF GRASSES 



The organs of grasses undergo 

 many modifications or departures 

 from the usual or typical structure. 

 A knowledge of the structure and 

 modifications of the organs, especially 

 of the parts of the spikelet, is essen- 

 tial for the interpretation of relation- 

 ships. 



VEGETATIVE ORGANS 



In size grasses vary from minute 

 species only 2 or 3 cm. high to the 

 giant bamboos 30 m. tall. The vege- 

 tative organs, however, consist, in all 

 cases, of root, stem, and leaves. A 

 single unbranched stem with the at- 

 tached leaves is a shoot. 



ROOT 



The roots of grasses are fibrous 

 with little modification. The primary 



root persists only a short time after 

 germination, its place being taken by 

 secondary roots produced from the 

 nodes of the young culm. Besides the 

 original root system at the base of 

 the plant, secondary roots are often 

 formed from nodes above the ground 

 as in maize (prop roots), or from the 

 nodes of creeping culms (rhizomes or 

 stolons). Roots are never produced 

 from the internodes of the culms. 



STEM 



The jointed stem of a grass, called 

 a culm, is made up of a series of 

 nodes and internodes. The internode 

 is hollow (wheat), or solid (maize); 

 the node or joint is always solid. The 

 culm may branch at the base as in 

 wheat (stools) or above the base as in 

 Muhlenbergia. Creeping culms, modi- 

 fied for propagation, may be below 

 ground (rhizomes) or above ground 

 (stolons). The lower internodes may 

 thicken into corms (timothy, species 

 of Melica, Arrhenatherum elatius var. 

 bidbosum), sometimes referred to as 

 bulbs. Perennial grasses may form a 

 sod or mass of individuals by means 

 of rhizomes or stolons, or they may 

 form a crown or tuft by the continual 

 formation of upright branches within 

 the lower sheaths. 



LEAF 



The leaves are borne on the culm 

 in two ranks, one at each node. The 

 leaf consists of sheath and blade. 

 The sheath envelops the culm above 

 the node, the margins overlapping 

 (open) or infrequently united into a 

 cylinder for a part or a whole of the 

 distance to the summit (closed). 



The blades are typically flat, nar- 

 row, and sessile. In dry regions they 

 are usually involute or convolute; in 

 tropical shade they are often com- 

 paratively short and wide (lanceo- 

 late, ovate, or elliptic); in most of 

 the bamboos they are narrowed into 

 a short petiole articulate with the 

 sheath. 



Some grasses (especially the Hor- 

 deae) bear, one on either side at the 



