FUNGOUS DISEASES. 53 



We may turn for a moment to one or two well-known diseases 

 which are very closely associated with abundant precipitation or a 

 humid atmosphere. There is no more conspicuous example than 

 the brown rot of stone fruits. Here is a fungus which, under 

 favorable conditions for propagation, has repeatedly carried off 

 practically the entire peach, plum, and cherry product of large 

 regions. It is well known that ten days or less of rainy, damp or 

 muggy weather as the ripening period of these fruits approaches 

 has often sufficed utterly to ruin the promise of a rich harvest. 

 The myriads of spores which break forth in tufts from the decaying 

 fruits spread with the utmost ease to neighboring trees and even 

 orchards, finding lodgment always most readily when two or three 

 fruits hang together, preventing ventilation and surface drying. 

 Again, it is under such conditions that the black rot of grapes has 

 invariably exhibited its greatest severity. Similarly, the potato dis- 

 ease, that is, the late blight or Phytophthora, and many other fungi 

 of the family of downy mildews spread with enormous rapidity 

 with moisture as a chief factor. The same could be said of some of 

 the anthracnoses and other tvj^es of disease-producing organisms. 



On the other hand, there are fungous diseases which profit 

 materially from severe alternations or contrasts of weather condi- 

 tions. During a season which shows droughty and rainy periods 

 such leaf blights as those of celery and strawberry thrive to the 

 greatest degree. In fact the alternation of rainy seasons may not 

 be essential if hot weather and heavy dews prevail. It is then 

 apparent that the plant supports some injured or drying leaves. 

 It is primarily upon such organs that we may look for the first seats 

 of such diseases. Finally, there are fungous diseases which, 

 under ordinary circumstances, seem to be wholly dependent for 

 inoculation or infection upon previous wounds in the host plant. 

 Among such organisms are many of the canker-producing fungi, 

 and even a greater number of the toadstools and punks of our shade 

 trees, as well as possibly some bacterial diseases. In a discussion, 

 therefore, of the effect of conditions of growth upon the host plant, 

 it may be well to bear in mind these general types of fungous attack. 

 To enumerate these more specifically, there are certain fungi which 

 are, or seem to be, specially endowed with the ability to enter 

 relatively vigorous growing organs of the plant. Among some of 



