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ECOLOGY 141 



resist evaporation. They include most grasses of swamps, 

 bogs, moist land along water-courses, and the inhabitants 

 of forest and woodland. Grasses that become weeds in 

 cultivated and waste soil usually belong to the meso- 

 phytes. In general they have flat blades and will endure 

 considerable alternation of conditions between a large 

 amount of soil moisture and a moderate amount of 

 drought. 



Familiar examples of mesophytes are the common cultivated 

 grasses, such as corn, the small grains, sorghum, sugar-cane, the 

 meadow grasses, common annual weeds, such as crab-grass and fox- 

 tail, and the shade grasses of the tropical forests. 



Certain areas of open grass land include a mesophytic 

 flora. Natural meadow land contains too much moisture 

 to be classed as prairie. Grass land which contains an 

 excess of water, but not enough to support strictly water 

 plants, may be classed as bog, swamp, marsh or slough. 

 The tundra of northern regions includes a large grass 

 element. It is open wet land — ^wet because the subsoil is 

 frozen and there is poor drainage. At high altitudes are 

 found mountain meadows that support a mesophytic 

 flora, even though the soil be dry, the low temperature 

 being the determining factor. 



178. Xeroph3rtes. — These are grasses that are fitted 

 to endure soil conditions in which the moisture content 

 is deficient. They are, in consequence of this deficiency 

 provided with especial adaptations to resist evaporation. 

 In xerophytes belonging to other families of plants, water- 

 storing organs are common, but among grasses this 

 adaptation is rare. 



Panicum hulbosum H. B. K., of New Mexico, is provided with 

 a corm which probably acts as a storehouse of moisture. The corms 

 at the base of some species of MeUca, and the chain of corms in 



