252 
THE ROOT 
Knees — projections on roots of cypress. 
Adventitious roots — those that grow in unusual positions, 
especially from the end of a cut stem. Geranium, willow, 
any “ slip.” 
219. The Duration of Roots. — Roots which live only for 
a season are called annual roots, examples of which are corn, 
peas, beans, and other 
common garden plants. 
Those that store the food 
manufactured one season 
and use it to produce 
flowers and fruit the next 
are called biennial roots. 
The garden furnishes ex¬ 
amples of these in the 
fleshy roots of carrots, 
parsnips, beets, turnips, 
and vegetable oysters. 
Roots that live from year 
to year, like those of trees, 
the dandelion, burdock, 
horse-radish, peony, and 
“ pie plant ” are perennial 
Figure 241. — Aerial Roots of Ivy. 
These are used for attachment, growing 220 Extent of Root 
only on the side towards the surface on 
Which the stem lies. System. — The root sys¬ 
tem of a tree growing in 
fertile soil is about equal to the parts above the ground. 
An oat plant has a root system the combined length of which 
is about 154 feet; a wheat plant has single roots seven feet 
long; and alfalfa an enormous root system (see Figure 244). 
A single root of alfalfa may extend more than 20 feet in one 
direction in a loose soil. 
221. Specialized Roots. — The roots of the ivy which 
grow for attachment differ from ordinary roots not only in 
