122 ATTEND IX. 



Microscopic Appearances. 



Mycelium. — Branching fibrils combined into a dense network. 

 This both in liquid and solid media. 



Spores. — At the end of the branches of mycelium, on free surfaces. 

 Spherical spores are produced in small pyramidal clusters by the 

 transverse division of the terminal twigs, into which the branches 

 break up at their ends. Spores are not formed except on free sur- 

 faces ; they are never found in growths from liquids, or from the 

 central portions of gelatine cultures. They are round, comparatively 

 large (7 /a.), and highly refractile. They take on aniline dyes easily, 

 as does also the mycelium. 



GENUS ASPERGILLUS. 



Several common species are included under this genus, and the 

 generic characters which unite them are the nature of the mycelium 

 and the nature of the fructification. The Aspergillus head, bearing 

 the spores, consists in all cases of a central club-shaped stem, upon 

 the surface of which the spores are placed. Slight differences in the 

 shape or colour of these basidia, and of the spores which they 

 support, determine the names and characters of the species into which 

 the genus is divided. 



A. albus (Eig. 24, p. 65). On Potatoes, Bread, Cheese, &-r. — A 

 pure white woolly looking growth, forming rounded masses, with a 

 very convex surface. 



In Gelatine. — On surface grows as on bread, but does not form so 

 typical a hemisphere as in that substance, the growth being flattened 

 on the surface, or even in some cases slightly concave. It does not 

 liquefy gelatine. In the centre of the jelly it forms spherical nodules 

 of a dull opaque colour, with a distinct limit to their growth peripherally. 



In liquids. — Found as rounded masses at bottom of beaker. 



Microscopically. — It has the characteristics of the genus above 

 described, both basidia and spores being quite free from pigment 

 granules. Its generally distinctive feature is its intensely white colour. 



A. repens (Figs. 25 and 26, p. 67). On Potato, &>c. — A sage-green 

 growth with a velvety surface, growing rapidly as a flat field over the 

 surface of the nutrient soil, and forming a layer not more that 0*25 cm. 

 thick. 



In Gelatine. — At surface forms colour due to spores ; in centre of 

 jelly grows as rounded white nodules, in which no spore formation 

 occurs. 



In liquids. — Floats as green layer on surface. 



Microscopically. — Like other species, except that in connection with 

 the spores there are fine granules of the green pigment. The pig- 



