90 EVOLUTION OF PLANTS 
duced from these spores upon the thorn (D) is abso- 
lutely different in appearance from that upon the cedar, 
the spores being very much smaller and produced in 
chains within curious cup-shaped receptacles, much like 
the barberry cluster-cups. These spores on being car- 
ried back to the cedar produce upon it the form which 
gives rise to the cedar-apples. This change of host in 
these parasites is exactly paralleled by the life-history 
of such animal parasites as Trichina and the tapeworms, 
which also require more than one host for their com- 
plete development. 
The more familiar of the larger fungi, such as toad- 
stools and puff-balls, are for the most part saprophytes, 
the vegetative portion, or mycelium, being buried in 
the substratum consisting of vegetable mould or earth 
rich in organic matter, where it feeds and grows, and 
finally sends up the spore-bearing fruit (spore-fruit, 
sporophore), which is the familiar toadstool or puff-ball, 
ordinarily supposed to be the whole plant. 
The Mycomycetes (apart from the lichens) may be 
arranged in three orders, which, however, show but 
little in common. These are the Sac-fungi (Ascomyce- 
tes); the Mushrooms and their allies (Basidiomycetes) ; 
and Rusts (cidiomycetes). 
THE ASCOMYCETES 
The distinguishing mark of this order is the produc- 
tion of spores in sac-shaped cells or asci, whence the 
name. In the lowest of the series, such as the fungus 
which causes the distortion of peach leaves known as 
“curl,” the spore-sacs are formed without any definite 
