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 (JEcidiomycetes). 



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 



