VEGETATIVE ORGANS OF GRASSES 



363 



of four months, while that of Poa compressa and Poa pratensis 

 was two weeks. 



3. A perennial grass is distinguished from an annual by the 

 presence of a rhizome. 



4. Rhizomes may be distingnished from roots by the presence 

 cf buds, nodes, intemodes, and scales. 



5. Elhizomes may be slender, terminating in a single shoot, 

 or producing several shoots. They may be creeping rhizomes or 

 rudimentary corms. In ease of Stipa spartea the old rhizome 



Fig'. 139. — A, cross section of rliizome, Poa compressa; B, outline cross 

 section of culm, Poa compressa: C, outline crosis section of culm, Poa pra- 

 tensis; T>, cross section of rhizome, Poa pratensis. 



dies, while the base of the old culm develops new shoots and 

 subsequently new rhizomes which are comparatively short. 



6. The roots of grasses are slender and fibrous, and vary m 

 the same species as to gross structure ; thus this is not a deter- 

 mining characteristic. 



7. The culms of grasses are erect, decumbent or creeping, 

 cylindrical or flattened. 



8. The leaf is composed of the sheath and blade ; the ligule is 

 formed at the junction of the blade aiid sheath; the collar is 



