92 EVOLUTION OF PLANTS 
The spore-fruit in these mildews is very simple, and 
in most cases is preceded by the formation of an archi- 
carp and antheridium (Fig. 24, B), both of which are 
simple cells cut off from special branches. These 
organs unite, and the contents, including the nuclei, 
fuse, and thus a true fertilization is effected, much as 
in the white rust described under the Phycomycetes. 
In the simplest of the mildews the fertilized archicarp 
divides into a few cells, one of which grows directly into 
an oval sac in which, after a preliminary division of the 
nucleus into eight, there is formed about each of these 
nuclei an aggregation of protoplasm which becomes sur- 
rounded by a cell-wall and forms a spore. There are 
still simpler Ascomycetes where the fertilized archicarp 
becomes at once transformed into the ascus. From the 
filaments close to the archicarp there grow out a num- 
ber of short branches which form a compact covering 
about the asci, the whole structure forming the “ peri- 
thecium ” or spore-fruit of the mildew. In many of the 
mildews the cells forming the wall of the perithecium 
develop hair-like appendages of curious and characteris- 
tic shapes, which constitute one of the best means of dis- 
tinguishing the different genera and species. 
Closely related to the mildews is the common blue- 
mould, Penicillium, and the herbarium-mould, Euro- 
tium. These are saprophytes, and the spores are borne 
on branching conidiophcres instead of in simple chains. 
The spore-fruit of some of the larger Ascomycetes 
is very conspicuous, and in the case of the pretty cup- 
fungi of various vivid colors, scarlet, orange, yellow, etc. 
These large spore-fruits are usually the product of a 
number of archicarps, i.e. they are compound in nature, 
