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 propagation—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. 
