100 A TEXT-BOOK OF GRASSES 



bamboos and a few other groups (such as Lasiacis and 

 Arundo) the culms are woody and persist many years. 

 Transitional forms are not uncommon, especially in desert 

 regions where the base of the culms becomes perennial, 

 the new shoots arising from this more or less elongated 

 and woody portion. 



125. Stems modified for prbpagation. — The usual 

 form of propagating stem is the rhizome or rootstock 

 (Fig. 58). Rhizomes are creeping underground stems 

 that may be distinguished from roots by the presence 

 of reduced leaves in the form of scales. The terminal bud 

 is hard and sharp so that the rhizome is able to force its 

 way through the soil. Rhizomes vary greatly in size and 

 consistency, being slender or almost thread-like in some 

 species and thick and firm in others, but are rarely suc- 

 culent enough to be called fleshy. From the rhizomes are 

 sent up the vertical shoots, sometimes a single shoot the 

 following season, sometimes several during the same 

 season. 



In sandy soil, especially on sand-dunes, the system of 

 rhizomes reaches its greatest development. Beach-grass 

 (Ammophila) and species of Spartina (such as S. juncea) 

 produce a branching network, a single element of which 

 may be many feet in length. Under favorable circum- 

 stances of isolation, a vigorous rhizome may be traced a 

 long distance by the line of vertical shoots produced. 

 Swamp-grasses are usually provided with a well-developed 

 rhizome system, by which they may form a layer over 

 soft mud or even upon the surface of water. 



Grasses that grow in ordinary alluvial soil and that 

 produce copious slender rhizomes form a firm sod and are 

 useful for lawns. 



Examples: Blue-grass and Bermuda-grass. 



