ECONOMIC IMPORTANCE OF GRASSES 



123 



Stems. The stems of grasses are divided into nodes and internodes 

 and are called culms (halms, 

 haulms). The nodes are 

 usually enlarged always solid 

 joints, while the internodes 

 are hollow (bamboo and most 

 other grasses), or solid (maize 

 and sugar cane). The under- 

 giound stems, or rootstocks 

 (rhizomes), are likewise jointed 

 and have sometimes, as in the 

 marram grass, a hard, sharp- 

 pointed, growing apex, which 

 enables the rootstock to push 

 its way through the resistant 

 soil. Occasionally, as in the 

 reed Phragmites communis of 

 our eastern fenlands, rhizomes 

 are found, as thick, as a 

 fountain pen, and 5.8 meters 

 long, enabling this marsh grass 

 to spread with great rapidity 

 in the occupation of new areas 

 of marshland. Two types of 

 branching of the erect stem 

 have been distinguished. The 

 extravaginal method is where 

 the new lateral branch breaks 

 through the sheaths of the 

 basal leaves of the stem giving 

 rise to horizontal branches. 

 This method of branching is 

 typical of the sod-, or turf- 

 forming grasses, and these 

 alone are suitable in the con- 

 struction Of lawns, croquet FIG- 46.-Wheat plant showing the general habit 



of grasses. (Robbtns.) 

 grounds and golf courses. The 



prairies of the middle west owe their closed turf to the presence of 



