448 A TEXTBOOK OF BOTANY [Ch. X 



groups, Ascomycetes and Basidiomycetes, which are fre- 

 quently treated together as Eumycetes or "true Fungi, " 

 though this name is often made also to include the Phyco- 

 mycetes. The relations of these groups to other Thallo- 

 phytes are obscure, some authorities deriving them from the 

 Red Algae, and others from the Phycomycetes. Since they 

 are mostly saprophytes or parasites upon land plants, they 

 probably represent the descendants of Fungi which ac- 

 companied the earliest plants from the water to the land 

 in their evolution from the Algae. Thus these Fungi have 

 had time for a long evolution upon their own account. 



The Ascomycetes and Basidiomycetes together comprise 

 some 50,000 to 60,000 species of Mildews, Mushrooms, 

 Lichens, Rusts, Smuts, and other conspicuous and important 

 forms, of which many are the cause of destructive plant 

 diseases. Vegetatively the two groups are much alike, the 

 plant body being commonly differentiated into two very 

 distinct parts. First there is the feeding mycelium, which, 

 while sometimes compact and thallus-like, or even dense 

 and hard (sclerotium), is commonly wide ranging and loose 

 branching in thin threads (Fig. 328), which penetrate the tis- 

 sues of a host, or else dead organic matter, including humus, 

 from which they draw their food in the usual manner (page 

 85). Second, there are the sporophores, typically stalked 

 structures (as in the Mushroom), which carry the spores 

 out into the air where the winds reach and scatter them. 

 These structures are composed of compacted or intertwined 

 threads, sometimes dense and hard. It is in the reproduc- 

 tion that the distinction exists between the two groups, 

 for in the Ascomycetes the characteristic structure is an 

 ascus or sac, containing typically eight spores. Numbers 

 of these asci develop together in an ascocarp, which is 

 either open cup-shaped (apothecium), or else flask- or globu- 

 lar-shaped (perithecium). This ascocarp typically forms 

 like the cystocarp of the Red Algse, — viz. as result of the 

 fertilization of an ascogonium (the procarp) through a tri- 



