(\)iX)RAi)o Plant Diseases 
15 
very probable that if the sexual spores were known they could 
be transferred to the Ascomycete group. In fact, the sexual spores 
have been discovered for many species of this group and as a result 
they have been transferred to their proper place among the Ascomy- 
cetes. The spores of the imperfect fungi as mentioned above are 
formed much as the asexual spores of the Ascomycetes. 
Flowering Plants — In addition to the bacteria, slime molds, and 
fungi there are a few higher plants wich draw their nourishment 
from other living plants and are therefore parasites. Mistletoe and 
Three methods of spore formation in the imperfect fungi, 
a — Sporodochium c — Pycnidium. b — Acervulus 
(a. after Tulasne; c. after Quaintance and Shear; b, after Smith.) 
dodder are the most common parasitic flowering plants. They obtain 
their food by sending root like structures (haustoria) into the tissues 
of the plant on which they are living and absorbing the already 
manufactured food. 
Insects and Other Animals — Many important and serious plant 
diseases are caused by insects, mites and other animals. This field, 
however, is best left to the Entomologist. Diseases produced by 
such organisms are not included in this bulletin. 
NON-PARASITIC DISEASES 
Among the agencies responsible for physiological or non-parasitic 
diseases may be mentioned unfavorable chemical and physical condi- 
tions of the soil, imfavorable climatic conditions and mechanical 
injuries. 
Unfavorable chemical conditions of the soil may be the result of 
either a deficiency or an excess of some element. The absence of 
