76 Plant Life and Evolution 



tents of one passes into the other and fuses with it. 

 The fertilized cell is stimulated into growth and 

 produces finally one or more sac-shaped cells, the 

 " asci " or spore sacs, within which are produced 

 usually eight spores. All of the typical sac-fungi 

 develop sooner or later spores of this type, 

 from which the class receives its name. The 

 spore sacs are only occasionally exposed, as for 

 instance in the fungus Exoascus, which causes the 

 disease of peach trees known as " leaf curl." Usu- 

 ally there is developed a protective envelope of sterile 

 tissue so that the spore sacs are contained in a defi- 

 nite fruiting body or " sporocarp," which may reach 

 considerable dimensions as in the scarlet cup-fungi 

 which are sometimes encountered in damp woods. 



While the development of this spore fruit may be 

 preceded by the fertilization of a definite " ascogo- 

 nium," in most of the large forms like the cup- 

 fungi this has not been demonstrated, and a true 

 fertilization is probably wanting. 



Basidiomycetes. The mushrooms, toadstools, 

 puff-balls, and rusts represent the second great di- 

 vision, or class of the true fungi, the Basidiomy- 

 cetes. In the large forms, such as the mushroom, 

 the spore fruits arise from the extensively developed 

 mycelium in the earth or rotten wood upon which 

 the fungus is growing. The spore fruits are often 

 of large size and characteristic form, and upon cer- 

 tain portions are borne the spores. In the mushroom 

 they arise from the surface of the " gills," the 



