318 THE PARASITIC DISEASES OF PLANTS 
the great influence of the weather upon the fungoid diseases. In 
moist weather the spores find plenty of moisture upon the surface 
of the leaves, while in dry weather the necessary moisture is 
lacking. Once it has germinated and its mycelium has entered 
the plant, it finds plenty of moisture within so that it is no longer 
dependent upon the weather. 
The effects produced by these fungi growing in the plant tissues 
are extremely varied. Any part of the plant may be affected, 
some diseases showing in one place and others elsewhere. The 
leaf may become covered with spots of various colors, or it may 
wilt, or roll up or drop off. Scabs may grow on the plant or its 
fruit, or the whole may show signs of rotting. Plant diseases have 
received various popular names that are loosely applied and 
not very clear in their meaning. The more common descriptive 
names are the following: 
Wilts are characterized by the wilting and withering of the 
plant. 
Rots are characterized by a tendency of the plant tissue to 
soften and decay. 
Smuts show a mass of black or blackish spores. 
Mildews show a whitish, powdery growth over the surface of 
the host. 
Rusts show spots of a reddish color, due to reddish-yellow 
spores. 
Anthracnose is a name frequently applied to diseases causing 
spots on the leaves or elsewhere. 
Blight is a term with no definite meaning, but is generally ap- 
plied to almost anything that causes a general wilting and de- 
struction of the plant. 
These terms are all in a measure descriptive terms of the effects 
produced by the parasites on the host. None of them are specific 
diseases, but all are produced by many different parasites on many 
different hosts, and in some cases the same parasite may produce 
different types of disease at different stages of its life. 
