UNDERGROUND STEMS 179 
node, will develop a new plant. Weeds of this type are multi- 
plied rather than destroyed by plowing and discing. 
Underground stems may be much elongated or they may be 
short and thick. In their subterranean habit, they resemble 
roots, and one may easily 
mistake some types of them 
for roots, unless the stem 
characters are well in mind. 
However, the presence of 
nodes, internodes, and 
leaves, although the latter 
are usually scale-like, serve 
to identify the underground 
structure bearing them as 
a stem. For example, the 
so-called eyes of the Irish 
Potato are buds and are lo- 
cated in the axils of small 
scales which mark the nodes 
of the tuber. (Fig. 1565.) 
On some the scale-like 
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VITV AT NY VAL AAA AAAI 
Fic. 154. — A Woodbine (Ampelopsis Fic. 155. — Irish Potato. 
climbing a stone wall. a, tendrils. e, eyes; s, scale leaves. 
leaves are large and fleshy, while on others they are very incon- 
spicuous. Underground stems differ so much that they have 
been classified into rhizomes or rootstocks, tubers, bulbs, and corms. 
Rhizomes are very much elongated underground stems. They 
are so named because of their resemblance to roots (the word 
rhizome meaning root-like). They are commonly called root- 
stocks. The rhizome is one of the most common forms of under- 
