UNDERGROUND STEMS 157 



the rhizome habit that makes some weeds so very hard to 

 kill out. The rhizomes of quack-grass, a common weed, 

 may be hoed to pieces, and still new plants will spring 

 up from the nodes. Among garden plants, asparagus and 

 rhubarb grow from rhizomes. It is evident that a rhizome 

 is both a reproductive and a nutritive organ. 



Rhizomes possess power to assume certain rather definite 

 positions in the soil. Each kind appears to do well at a 

 certain depth, and, if changed from that depth, will grow 

 up or down until the proper depth is attained again. Thus 

 if a trilUum rhizome is transplanted and not put at the 

 right depth, it will grow up or down until its particular 

 soil level is reached. It will then begin its horizontal 

 growth again. The causes of this kind of response are 

 not well understood. 



By growth forward and death behind rhizomes gradually 

 progress through the soil, putting up new shoots from 

 season to season as they go. Occasionally they branch. 

 When death reaches the point of branching, the branch is 

 severed from its parent and thus separate rhizomes are 

 produced. . It is evident that this rhizome habit of repro- 

 duction has some advantages over the seed habit. Indeed 

 some plants are reproduced by their rhizomes far more 

 than they are by seeds. The bamboo, for example, pro- 

 duces flowers and seeds only about once in twenty years, 

 apparently having given up the seed habit, almost entirely 

 in favor of the rhizome habit. ' Taking plants in general, 

 hundreds of seeds die for one that develops. This great 

 loss is chiefly due to the fact that on ground already occu- 

 pied by other plants it is next to impossible for the seed- 

 ling to get its root into the ground and at work before its 

 food reserve is consumed. This difficulty, however, is no 



