14 FIRST BOOK OF GRASSES 



grass (Poa pratensis, Fig. 9) furnishes an excellent 

 example. Sometimes the rhizome is thick and woody, 

 sending up shoots from its nodes, the whole forming a 

 dense colony, as in gama-grass (Tripsacum dacty- 

 loides). A rhizome, being a stem, is jointed and 

 bears scales, which are reduced leaves. By these it 

 may always be distinguished from a root, which 

 is not jointed and never bears scales. In some 



grasses the shoots 

 borne at the base 

 of the culm are 

 on the surface of 

 the earth instead 

 of beneath it. 

 Such shoots are 

 stolons, or run- 

 ners. These, like 

 rhizomes, are 



FIG. 9. Base of plant and underground parts, jointed and bear 

 roots and rhizomes, of Poa pratensis. 



scales or, some- 

 times, well-developed leaves. Rhizomes and stolons 

 both bear roots at the under side of the nodes. In a 

 few species, Bermuda-grass for one, a plant may 

 produce either rhizomes or stolons according to the 

 conditions under which it is growing. There is no 

 real difference between a rhizome and a stolon, the 

 one is below ground and colorless, the other above 

 ground and green. 



Culms are hollow in most grasses, but in corn, 

 sugar-cane, sorghum, and related grasses they are 



