YEASTS AND MOULDS. 581 



Saccharomyces niger (Black Torula). Cells also present 

 in the air. Cultivated in nutrient gelatine they form a black 

 crust (Fig. 231). 



MOULD-FUNGI OR HYPHOMYCETES. 



The mould-fungi have been divided into 

 five orders : Hypodermii, Phycomycetes, Asco- 

 mycetes, Basidiomycetes and Myxomycetes. 

 The following species, with the orders to 

 which they belong, are of especial interest : 



HYPODERMII. 



Ustilago carbo (Mildew, Smut). Spores 

 brown, circular ; episporium smooth ; sporidia, 

 ovoid cells. The spores or conidia occur as 

 a black powder in the ears and panicles of 

 wheat, barley and oats. 



Tilletia caries. Spores round, pale 

 brown ; episporium with reticulated thicken- 

 ings. In germinating, the sporidia grow 

 out radially from the end of the promyce- 

 lium ; these, at their lower part, conjugate p ^ 231 _ BLACR TQR . 

 by a cross branch and separate from the ULA> p URE CULTIVA- 

 promycelium, and at some point of the pair TION ON POTATO. 

 a hypha grows out, on which abundant 



secondary sporidia develop. The latter are long, oval cells, which 

 can in turn germinate. The fungus occurs in the form of a 

 stinking powder in grains of wheat, which renders the meal im- 

 pure, and gives it a disagreeable smell. 



Urocystis occulta. The spores consist of several cells united 

 together; partly, large dark-brown cells in the interior, and out- 

 side, several flat, semicircular, colourless cells. The promycelium 

 germinates as in Tilletia, but the cylindrical cells produce a hypha, 

 without, as a rule, previous conjugation. They occur as a black 

 powder in rye-straw in long disintegrated stripes, which are at first 

 greyish. The affected plant produces abortive ears. 



Empusa muscse. A spore or conidium of this fungus 

 alighting upon the white area of the under surface of the body 

 of the house-fly germinates into a hypha. The latter, penetrating 

 the skin, forms toruloid cells, which multiply by germination, and 

 are disseminated in the blood throughout the body of the fly. 



