MONOCOTYLEDONS 



431 



comprising the principal 

 vegetation of the meadows, 

 plains, marshes, and slopes 

 of this and other countries. 

 They are therefore either 

 mesophytic, hydrophytic, or 

 xerophytic. 



Many of the grasses per- 

 petuate and spread the 

 species by means of under- 

 ground stems in the form 

 of either rootstocks or stolons, 

 which enable them to form 

 dense mats and sods wher- 

 ever they gain a foothold 

 (Fig. 278). The leaves are 

 characteristic of monocoty- 

 ledons generally, being long 

 and -strap-shaped, with par- 

 allel veins. The flowers are 

 highly modified, and the 

 fruit in the true grasses 

 and cereal grains is an 

 achene, known as the cary- 

 opsis, or grain. 



FIG. 278. Habit of the couch grass, a weed pest 



Note that the aerial stems spring from nodes of the underground rhizome. When the 

 rhizome is cut in pieces, each node can reproduce a new plant and so spread the weed 



Economic importance. The true grasses are of the greatest 

 importance in furnishing pasturage and hay for animals and in 

 providing a good turf for lawns and meadows. The cereal grains, 

 including corn, wheat, oats, and rye, are all grasses which have 



