MORPHOLOGY OF THE VEGETATIVE ORGANS 97 
from rhizomes or rootstocks. These are modified shoots 
that burst through the sheaths and creep horizontally 
below the surface of the soil. Grasses such as the blue- 
grass, with well-developed rhizomes, tend to form a com- 
pact sod. The young shoots or innovations of such grasses 
are sometimes referred to as extravaginal. The various 
forms assumed by rhizomes will be discussed under the 
subject of the stem. 
Besides these two chief kinds of perennial grasses, 
there are those (such as the buffalo-grass) that produce 
stolons by which a sod is formed. Still another method of 
persisting through unfavorable seasons is found in many 
grasses growing in the water or mud. The lower prostrate 
or decumbent portion branches freely and persists while 
the upper portion dies back. The older portion dies sooner 
or later so that the original base of the plant disappears 
and one finds only a tangled mass of creeping and root- 
ing stems. 
The stems of grasses vary in height from an inch or 
less to several feet in herbaceous species. Some of the 
larger bamboos arise to the height of over 100 feet and 
may be a foot in diameter. Certain climbing species 
clamber up through the branches of trees to the height 
of 30 feet or more. 
121. Distribution—Grasses are found in all parts of 
the world where there is sufficient soil to permit growth. 
They are found from the tropics to the arctic regions, 
from sea-level up to the limits of perpetual snow. They 
are found in woods, plain, swamp and desert, on the floor 
of the deepest forest, on the sandy seashore, in moist 
gorges and on rocky cliffs. In the main, however, grasses 
love sunlight, and are found in greatest abundance in 
open land such as prairies and pine barrens. In mangrove 
G 
