SAPROPHYTES. 
DURATION OF ROOTS. 133 
they grow ; others, again, continue throughout their life to derive 
a portion of their food by means of roots imbedded in the soil. 
It will thus be seen that parasites differ from other plants in 
the fact that they do not live like them entirely on inorganic 
matters, but derive at least some of their food in an assimilated 
state from the plants on which they grow. Thus, when green 
like the Mistletoe, they obtain a portion of their food, like 
ordinary plants, from the air ; but if of other colours than green, 
all their food is derived by their roots from the plants on which 
they grow. It must also necessarily happen that parasites, by 
living partially or entirely upon those plants on which they are 
placed, frequently injure, and even destroy them, and in this 
way great damage is done to Clover, Flax, and other crops in 
this country and elsewhere. 
Besides the parasites just described, there is also another 
class of plants called saprophytes, which, whilst agreeing with 
ordinary parasites in deriving their food from already formed 
organic material, differ from this latter class in growing on dead 
organic substances, and therefore assimilating such matter which 
is in a state of decomposition or decay. Such plants as Mono- 
tropa Hypopithys, Corallorhiza innata, Epipogium Gmelini, and 
Neottia Nidus-avis, together with the greater number of Fungi, 
are examples of Saprophytes. 
Duration OF Roots.—Having now described the general 
characters and structure of the true or primary root, and of the 
adventitious or secondary root, we have in the next place to 
allude to certain differences which roots present depending upon 
their duration. Roots are thus divided into annual, bienwal, 
and perennial. 
1. Annual Roots.—These are produced by plants which grow 
from seed, flower, and die the same year in which they are 
developed. In such plants the roots are always of small size, 
and either all spring from a common point as in annual Grasses 
(fig. 259), or the true root is small, and gives off from its sides 
a number of small branches. Such plants, in the process of 
flowering and ripening their fruits and seeds, exhaust all the 
nutriment they contain, and thus necessarily perish. 
2. Biennial Roots.—These are produced by plants which 
spring from seed one year, but which do not flower and ripen 
their seeds till the second year, when they perish. Such roots 
are commonly enlarged in various ways at the close of the first 
season, in consequence of their tissues becoming gorged with 
nutritious matters stored up for the support of the plant during 
its flowering and fruiting the succeeding season. The Carrot 
(fig. 267), and Turnip (fig. 269), afford us good examples of 
biennial roots. 
3. Perennial Roots.—These are the roots of plants which live 
for many years. In some such plants, as the Dahlia (fig. 263), 
and Orchis (figs. 261 and 262), the roots are the only portions 
