SPECIAL FUNCTIONS AND FORMS OF STEMS 87 
like that of the May apple (fig. 69), the mints, couch grass, and 
many other plants, and some stouter kinds, like that of the tril- 
lium and Solomon’s-seal, are known as rvotstocks, or rhizomes. 
The very short shoots with disk-like stems and a covering of 
scales, or of coatings formed by thickened bases of leaves (famil- 
iar in some lilies, the tulip, and the onion), are called dubs. 
Much like bulbs, except that the stem is more developed and that 
the scales are almost lacking, are tubers. like those of the Jeru- 
salem artichoke, the potato, and the crocus.!. The potato is a 
particularly good tuber for study, as it has well-defined nodes 
and internodes; the buds (eyes) are arranged in a distinctly 
spiral manner and are borne in the axils 
of little scales which represent leaves, 
and not infrequently the tuber is con- 
siderably branched. 
85. Reproduction by portions of the 
stem. Some plants naturally reproduce 
themselves mainly by more or less spe- 
cialized portions of the stem, and in a 
cultivated state many others are made 
to do so. There are numerous kinds, 
such as the potato, the strawberry, the 
banana, and most lilies, that are almost 
always propagated by some sort of stem 
or shoot. 
Many plants bear small aérial bulbs 
: 2 cot, cotyledons; st, tuber- 
or tubers on some portion of the stem hearing underground stems: 
and are commonly reproduced by these. 4 very small tubers; 7, 
. ae . root. Three fourths natu- 
Familiar examples among cultivated “yal size. After Percival 
plants are the onion and the tiger lily. 
The bulblets known as onion sets are for sale at every seed 
store, and in some parts of the country are almost exclusively 
planted by onion growers, while in other sections the seed is 
more generally planted. The black bulblets of the tiger lily 
ea5 
"6 
Fie. 70. A potato seed- 
ling ten weeks old 
1 Such very short underground stems as that of the jack-in-the-pulpit and 
the crocus are often called corms. 
