SPECIAL FUNCTIONS AND FORMS OF STEMS 89 



Underground stems of various kinds are so common as 

 means of reproduction that only a very few of them need be 

 mentioned. Some of the worst weeds are those which have 

 running rootstocks, 

 like the nut grass 

 ( Cyperus), which 

 produces many lit- 

 tle tubers, each of 

 which may grow 

 into a new plant, 

 and the couch 

 grass (Chapter XX) 

 and Canada thistle, 

 which may be cut 

 up by the hoe 

 and produce a new 

 plant from every 

 node. Among cul- 

 tivated plants a 

 great number of the 

 earliest blooming 

 herbaceous kinds, 

 such as squills, 

 hyacinths, tulips, 

 crocuses, and snow- 

 drops, are grown 

 from bulbs or other 

 forms of under- 

 ground stem. The 

 commonest of all 

 instances of propa- 

 gation by this kind 

 of stem is that of the potato (figs. 70 and 71), which is never 

 grown from seed except for the production of new varieties. 

 As every fanner and market gardener knows, each potato 

 will produce as many new plants as it has buds, or eyes, 



FIG. 72. A black raspberry plant reproducing by 

 a natural stolon 



At A, the original root system ; at B, a newly formed 

 root system with a young shoot sh. Much reduced and 

 somewhat diagrammatic. The arch is really much 

 flatter and the dying portion of the stem, aa', propor- 

 tionally five or ten times as long as here shown 



