194 
THE PLANT WORLD. 
result is always the same, namely, the loss of the power of utiliz¬ 
ing food. Such a condition is in fact one form of starvation, and 
the final result, so far as the plant is concerned, is the same. 
Roots are sometimes destroyed by insects, moles or other bur¬ 
rowing animals. The principal function of roots is to absorb 
water and food matters from the soil, so that the loss of roots 
implies the loss of the power to absorb water and such foods 
as are in the soil water. A tree whose roots have been eaten off 
is in danger of dying from thirst as well as from starvation. 
But many trees suffer from the loss of their roots at the hands 
of man himself, when he digs them out in such a way as to cut 
off the roots close to the base of the trunk. A tree so mutilated 
is in as pitiable a condition as when it has suffered such a loss 
through other means. The mere fact that the owner of the tree 
has purposely cut off the roots does not help the poor tree. It 
is quite as likely to die from thirst and starvation as though 
the mutilation had been done by rascally gophers or moles. 
Sometimes the flowers of apple trees suddenly die before the 
fruit has formed. Here the disease is confined to the reproductive 
organs, and while the life of the tree itself is not threatened, the 
crop of fruit is ruined. This disease is often due to a form 
of “ blight,” closely related to, if not identical with, the ordi¬ 
nary “ blight” of twigs and leaves. In other cases it is due to the 
presence of small worms (larvae) which eat the soft tissues of 
the flower stalks and bases, killing the whole cluster much as 
in the case of the blight. 
6 . Fungi .—Here we come to the most fruitful causes of plant 
diseases. There are so many species of harmful fungi that every 
.kind of higher plant is infested by at least several, and some are 
attacked by ten times as many. These affect plants in different 
ways, but for my present purpose I shall notice only the follow¬ 
ing modes: ( a ) Some grow over the surface of the leaves 
choking them so that they cannot perform their functions prop¬ 
erly. A good example of such a surface fungus is the Powdery 
Mildew which often attacks the leaves of roses, verbenas, cherries, 
etc., covering them with a fine white powder. Every observing 
man knows, that plants so affected cannot make a good growth. 
