266 HOW CROPS GROW. 
represented in fig. 46, which infests so many farms. Each 
node of the root-stock, being usually supplied with roots, 
and having latent buds, is ready to become an independ- 
ent growth the moment it is detached from its parent 
plant. In this way quack-grass becomes especially troub- 
Fig. 46. 
lesome to the farmer, for, within certain limits, the more 
he harrows the fields where it, has obtained a footing, the 
more does it spread and multiply. 
Suckers.—The rose, raspberry, and cherry, are examples 
of plants which send out subterranean branches, analogous 
to the root-stock. These coming to the surface, become 
aérial stems, and are then termed suckers. 
The Tubers of most agricultural plants are fleshy en- 
largements of the extremities of subterranean stems. 
Their eyes are the points where the buds exist, usually 
three together, and where minute scales — rudimentary 
leaves—may be observed. The common potato and arti- 
choke are instances of tubers. Tubers serve excellently 
for propagation. Each eye, or bud, may become a new 
plant. From the quantity of starch, etc., accumulated in 
them, they are of great importance as food. The number 
of tubers produced by a potato-plant appears to be in- 
creased by planting originally at a considerable depth, or 
by “hillmg up” earth around the base of the aérial stems 
during the early stages of its growth. , 
