26 



EUMYCETES 



infected insects. A spore which finds its way to a suitable insect germinates. 

 putting out a hypha which penetrates into the body of' the victim, and there 

 sprouts in a veast-like manner, producing a large number of separate cells. 

 Death soon follows, and then each yeast-like cell produces a hypha which 

 grows out through the skin of the insect, and then forms, at its apex, a single 

 conidium. It has been attempted to use this fungus as a means of destroying 

 locusts ; hut so far this has not been generally practicable, mainly owing to 

 the tact that the fungus cannot be cultivated as a saprophyte on any of the 

 ordinary media. 



Class II. Ascomycetes. 



This class is primarily characterised by the formation of' a special repro- 

 ductive organ, the ascus, in which almost invariably eight ascospores are 

 produced. Other methods of reproduction are often met with in addition. 



Three sub-classes may be conveniently recognised, based on the structure 

 of that part on or in which the asci are round : 



A. Perisporiales. Asci completely enclosed in a cleistoCCLVp. 



B. Pyrenomycetes. Asci in a flask-shaped cavity, open only at the 



apex, the peritheciwvn. 



C. Discomycetes. Asci on the concave, upper surface of a saucer 



or cup-shaped structure, the apothecium. 



In addition there are a few forms in which the asci either do not contain 

 the typical, definite number of spores, or are borne directly on the mycelium. 

 The yeast plant is the most important of these. 



Sub-class A. Perisporiales. To this sub-class belong some of the 

 blue-green moulds (mostly saprophytic), some parasites of plants, viz. the 

 mildews of the vine, tobacco and vegetable marrow, and lastly the edible 

 truffles {Tuber brumale and T. aestivum of Central Europe), the fruit bodies 

 of which occur underground. 



Two indigenous species of truffles, belonging to the genus Tcrfezia, are 

 found in the Kalahari, occurring near shrubs of Acacia hcbcclada, generally 3 — 4 



4^ 



Fig. 19c/. Terfezia Claveryi Chatin. From neighbourhood of Windhuk. Side view ami 

 transverse sect ion. 2/3 nat. size. Photo, by Frau C. Bohr 



