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 anew 
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 
Fic. 72. A black raspberry plant reproducing by 
a natural stolon 
At 4, the original root system; at B, a newly formed 
root system with a young shoot sk. 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 
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 farmer and market gardener knows, each potato 
will produce as many new plants as it has buds, or eyes, 
