148 A TEXT-BOOK OF GRASSES 



188. Distribution of grasses. — As stated in a preceding 

 paragraph (Par. 121), the grasses are represented in all 

 parts of the earth's land-surface where the conditions are 

 suitable for the growth of flowering plants, from sea-level 

 to the snow-line on the high mountains, from Greenland 

 to the antarctic continent, from swamp to desert, and 

 from the deep forest to the clefts of the boldest cliff. The 

 great tribes Andropogoneae and Panicese predominate in 

 the warmer regions, while the Agrostideae and Festuceae 

 predominate in the cooler regions. Space will not permit 

 of detailed references to the distribution of genera and 

 species. Small genera are often much restricted in their 

 area while large genera are usually distributed over a 

 wide area. The great genera Andropogon, Panicum, 

 Paspalum and Eragrostis are found throughout the tropics 

 of both hemispheres. Muhlenbergia and Bouteloua, also 

 large genera, are confined to the American continent and 

 are especially well represented on the Mexican plateau. 

 Poa and Festuca are found in all continents, but mostly 

 in the cooler regions, extending to the northern and 

 southern limit of vegetation, and well represented in 

 alpine regions, even of the high mountains of the tropics. 



189. Distribution of species. — Species also vary greatly 

 as to the extent of the area in which they are found. 

 Certain agressive species known as weeds are now wide- 

 spread over extensive areas of both hemispheres. Crab- 

 grass (Syntherisma sanguinalis) and goose-grass {Eleusine 

 indica (L.) Gaertn.) are familiar examples. Heteropogon 

 contortus (L.) Beauv. is an example of a similarly wide- 

 spread species which is native throughout its area. Many 

 species of the seashore and of marshes are likewise exten- 

 sively distributed. Spartina glabra Muhl. and Ammophila 

 arenaria are found on the seacoast of Europe and America, 



