248 



THE FUNGI 



are such forms as Vaucheria (Sec. 228), and other types of 

 the Siphonales, and some authors believe that the molds, water 

 molds, and blights have been derived from that general region 

 of the algas. 



CLASS VIII. THE SAC FUNGI, OE ASCOMYCETES 



265. The sac fungi. The sac fungi are distinguished by a 

 peculiar type of reproduction, through spores which are devel- 

 oped, generally eight in number, in a special unicellular organ 

 called an ascus (plural, asci), which means 

 a sac. The asci are produced sometimes 

 in very great numbers in a fructification 

 termed an ascocarp, or sac fruit, which is 

 a structure of importance. The filaments, 

 or hyphse, of the sac fungi are divided by 

 cross walls into cells, and are never long 

 coenocytes, as in the alga-like fungi (Phy- 

 covtiycetes). The Ascomycetes is one of the 

 two largest groups of the fungi, comprising 

 more than fifteen thousand species. We 

 can only describe a few forms from the 

 following groups : (1) the mildews, (2) the 

 cup fungi, and (3) the knot and wart fungi. 

 FIG. 218 Sac fruits (as- 266 The mildews. The true mildews 



cocarps) of the lilac 



mildew (Microsphcera (order Perisporiales) are a very clearly de- 



Alni) on the lower sur- fined group of fungi, and it is desirable 

 face of a lilac leaf thafc the term mMew be restricted to 



them. They are mostly external parasites, very common 011 

 the leaves of many seed plants, such as wheat, lilac, Virginia 

 creeper, grapes, verbena, cherry, oak, willow, etc. The hyphse 

 form a cobweb-like growth (mycelium) over the leaves, and put 

 forth sucker-like processes called haustoria, which enter the 

 epidermal cells of the host. There is a method of rapid multi- 

 plication during the summer months by air spores, or conidia, 



