DISEASES OF CULTIVATED PLANTS 347 
under such conditions will involve increased risks. The necessity 
for drainage will usually be apparent and due consideration of the 
limits of certain orchard trees needs also to be given. Cherry trees 
and even peach and apple trees will not survive under moisture con- 
ditions wherein plum and pear trees may grow with profit. 
Orchard replants in “‘clinker’”’ locations wherein failures have 
been numerous, will raise these questions of root-rots and relative 
adaptability of different orchard trees. Rotation planting, as pear or 
plum after apple, plum after cherry, etc., may at times succeed and 
replace unsightly gaps in the orchard by flourishing trees of another 
sort. At present, drainage and aeration are our known methods of 
restricting root-rots under out-door conditions. 
PARASITIC FOLIAGE DISEASES 
Foliage diseases of every sort are caused by oxygen loving or 
aerobic species of parasites, and very often this development on the 
leaves consists of the imperfect forms of the fungus life history. 
These forms are none the less aggressive and injurious for this 
reason, but the exact manner of survival from year to year becomes 
important wherever not known.. ‘The application of this to prevent- 
ive measures in the control of these diseases upon foliage and fruit 
is seen in the case of apple scab, the monilia rot of plums, peaches, 
cherries, etc., and in apple bitter-rot. These last two rot troubles 
survive in the “mummy” or dry rotted fruits and this explains the 
reason for the oft repeated injunction to destroy all “‘mummies” in 
addition to spraying operations. ‘The bitter-rot of apples is propa- 
gated by means of summer branch cankers on the tree, as brought 
out-in recent years. Other leaf forms survive on the fallen leaves 
or possibly in bud scales as with the leaf curl and “‘bladders”’ of the 
Exoascae. A large number must live over on the branches. 
Parasites upon foliage soon become apparent from the 
spots on the leaves and dropping of fruit resulting. This dropping 
may come asaresult of impaired vigor by reason of disease—‘hen 
it is later, but is more often the direct result of parasitic attack by 
the disease upon the young fruits. Herein as elsewhere the philoso- 
phy. of fungicides comes to our relief. A good foliage fungicide is a 
relatively insoluble compound which will not greatly injure the 
leaves with which it is in contact. The remedies for foliage troubles 
are applied in anticipation of attack and for the purpose of checking 
the fungus when it may appear. ‘The relative efficiencies of various 
fungicides in early summer will possibly depend upon the sticking 
qualities of the sprays. 
