Colorado Plant Diseases 
13 
Typical spore bearing 
organs of an Ascomy- 
cete ; two asci, each bear- 
ing eight ascospores. 
(After de Bary.) 
cup-shaped 
The Ascomycetes 
are distinguished 
from all other fungi 
by the fact that every 
member of the group 
has some of its spores 
(those formed by a 
sexual process) 
formed inside of 
characteristic sacs 
known as asci. The 
asci always contain a 
definite number o f 
spores (ascospores), 
usually eight. The 
asci are borne in 
special spore cases. 
These spore cases are 
in some forms and spherical or ball-shaped in others. 
In addition to ascospores several other kinds of spores may be 
formed. These are usually without a sexual process and have a 
variety of forms. Some are borne free on the mycelium and are 
known as conidiospores or conidia. The mycelium on which conidia 
are borne are sometimes grouped together in the tissue of a plant, 
forming a compact mass and giving rise to a structure known as a 
pustule or acervulus. 
Other spores are borne in spherical or flask-shaped spore cases or 
pycnidia. Spores borne in a pycnidium are called pycnospores. 
(A. after King; B. after Longyear.) 
The Ascomycetes are not as 
dependent upon water as the 
Phycomycetes and never form 
zoospores. They make up the 
largest group of fungi and a 
great many of them are plant 
parasites. Peach leaf curl, plum 
pocket, brown rot of peaches, 
ergot of rye, leaf spot of alfalfa 
and the powdery mildews of 
many crops are some of the 
numerous diseases caused by 
fungi of this group. 
