146 A TEXT-BOOK OF GRASSES 



to collect in depressions or drainage basins where the 

 water from showers remains longest. 



185. Halophjrtic grasses are those that grow in soil 

 containing an excess of mineral salts. In general they are 

 known as salt-marsh plants. They are found in the salt- 

 marshes of the seacoast and of interior alkali regions. 

 The soil that supports halophytes may not be lacking in 

 water, but the presence of soluble salts increases the 

 density of the soil-water and hence renders it less easily 

 absorbed by the root-system of the plant. Although 

 growing in water or wet soil, the plants have difficulty in 

 obtaining the necessary water-supply and consequently, 

 to avoid injury from loss of water through evaporation, 

 xerophytic characters have been developed. Among these 

 characters may be mentioned harshness due to the pres- 

 ence of mechanical tissue, roll-leaves, and succulence. 

 Familiar examples of halophytic grasses are Spartina 

 glabra Muhl. of the Atlantic coast salt-marshes and 

 Distichlis spicata (L.) Greene of the interior alkali plains. 



186. Hydrophytes are water plants. They grow in 

 the water, either submerged or from soil that is perma- 

 nently saturated. Only a few grasses, such as Hydrochloa 

 caroUniensis Beauv., are nearly or quite submerged. But 

 there are many that inhabit permanent fresh-water or 

 brackish marshes. To this group belong Zizania palustns 

 L. (Indian rice), Zizaniopsis miliacea (Michx.) Doll & 

 Asch., Paspalum dissectum L. and P. repens Berg. Pani- 

 cum elephantipes Nees and Echinochloa sahulicola Nees 

 of the American tropics are succulent hydrophytes, grow- 

 ing in several feet of water. Paspalum repens, of Pan- 

 ama, forms long runners that float upon the surface of 

 the water, buoyed up by their inflated sheaths. 



Swamp-grasses as distinguished from marsh-grasses 



