APPENDIX. 225 



Myxomycetcs. The following species, with the orders to 

 which they belong, are of especial interest. 



HYPODERMIL 



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 ; epi- 

 sporium with reticulated thickenings. In germinating 

 sporidia grow out radially from the end of the promy- 

 celium ; these, at their lower part, conjugate by a cross 

 branch, and separate from the promycelium, and at some 

 point of the pair, 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 impure, 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 outside several flat semi-circular, colourless 

 cells. Spores '024 mm. Promycelium germinates as in 

 Tilletia, but the cylindrical cells produce a hypha, without, 

 as a rule, previous conjugation. Occurs as a black powder 

 in rye straw, in long disintegrated stripes, which are at 

 first greyish. The affected plant produces abortive ears. 



Empusa muscae. Spores, -on mm. in diam. 

 A spore or conidium 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 toru- 

 loid cells, which multiply by germination, and are dissemi- 

 nated in the blood throughout the body of the fly. These 

 cells again grow into hyphae, which penetrate the skin, 

 each forming a conidium, which is cast off* with consider- 

 able force. The parasite is fatal to flies, especially in the 



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