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 



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