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TEXTBOOK OF BOTANY 



the West Central States grasses ha\'e been employed in stabilizing wind- 

 blown farm lands ( Fig. 181 ) . 



Pieces of rhizomes are often planted in preference to seeds. Rhizomes 

 of each species grow at a fairly definite depth below the surface of a 

 particular soil ( Fig. 182 ) . If they are planted below or above this depth 

 they grow up or down to the specific soil le\'el. 



When weeds, such as couch grass, bindweed, flowering spurge, and 

 nettle, grow among crop plants, their rhizomes may be broken and scat- 

 tered when the crops are being cultivated, and the weeds become still 

 more abundant. 



Fig. 183. The groundnut {Apios tuberosa) has many edible underground tuber.s 

 from which aerial shoots develop. 



Tubers. The tubers or thick terminal portions of rhizomes of Irish 

 potato are a means of vegetative multiplication common to many herba- 

 ceous plants (Figs. 183 and 184). The wild species of potato are native 



