390 THE GRAMINALES 



mation of other leaves. The curious screw-pines, Pandanus, a 

 large group from the oriental tropics and frequently seen in con- 

 servatories, belong to this order, also the bur reeds {Spar- 

 ganium), common about marshes and water ways, which are 

 the highest members of the order. 



131. Graminales, the Grass and Sedge Order. — This is one of 

 the largest groups of the Spermatophyta, some 7,000 species 

 being known, and in number of individuals it exceeds all others 

 (Fig. 282). These plants are almost universally distributed 

 over the earth and have become adapted to almost every condi- 

 tion of climate and soil. The ability of these plants, which are of 

 aquatic origin, to establish themselves upon the drier and more 

 diversified land surface doubtless promoted variations and ac- 

 counts for in part the enormous display of forms. The Grami- 

 nales and the palms (Principales) which belong to an order 

 related to Typha are about the only groups of monocotyledons 

 that are associated in sufficient numbers to form striking features 

 of the vegetation of a country. This is particularly true of the 

 Graminales in all lands, where they constitute the principal vege- 

 tation of hills, plains, meadows and marshes. These plants are 

 also of the greatest economic importance, furnishing a variety 

 of foods, as wheat, rye, barley, oats, rice, corn, hay, etc. The 

 bamboo also belongs to the order. The stem in the majority 

 of forms is a rhizome (as in Typha), which branches extensively 

 through the soil and sends up numerous aerial branches (Fig. 282, 

 B). These interwoven rhizomes, with their numerous roots, form 

 the firm swards of meadows and prairies. The aerial stems are 

 models of mechanical construction. The ability of the long 

 hollow stems of the grasses to support the heavy head of grain 

 must appeal to every one. An examination of Fig. 282 will 

 show you how the stem is reinforced by the long sheathing base 

 of the leaves while tough, elastic strands of stereome fibers are 

 so distributed as to give the best mechanical support. An un- 

 usual localization of the growing regions also characterizes the 

 grasses which enables them to lift up again their stems if they 

 by any means become prostrate. In case the stem become pros- 

 trate, the stimulus of gravity causes a renewal of growth in the 



