90 INTRODUCTION TO BOTANY 
though it is better not to cut the potato into too small pieces 
for propagation, or the plants will grow slowly at first. 
Why are potatoes almost always grown from the tuber 
rather than from seed? Why are plants of the Lily family 
Fic. 73. A willow cutting 
The roots are a little more than two 
months old. Somewhat reduced 
grown from bulbs ? 
86. Stolons, runners, and cuttings. 
Some plants, as the black raspberry 
(fig. 72), are naturally propagated 
by recurved branches which root 
wherever they touch the earth. 
Such rooting branches are called 
stolons. An artificial modification 
of this process (called layering), 
sometimes made use of in growing 
apples, pears, plums, and quinces, 
consists in bending down branches 
and covering portions of them with 
earth until they become well rooted. 
Runners, like those of the straw- 
berry, are very slender, nearly leafless, 
stolons. 
Cuttings are twigs or branches 
cut off, set in the earth, and kept 
there until they become well rooted 
(fig. 73). Numerous woody plants, 
such as willows, grapevines, currant 
bushes, gooseberry bushes, and gera- 
niums, and some herbaceous plants, 
such as the hopvine and the Wan- 
dering Jew, are usually grown from 
cuttings. Many others, such as the 
French marigold and the garden portulaca, not usually thus 
grown, may be readily propagated by cuttings. In the case of 
woody plants the cutting should be taken from well-matured 
twigs of the previous season. To avoid wilting, leafy cuttings 
are often kept covered for a time with a tumbler or bell glass. 
