120 NON-PATHOGENIC MICRO-ORGANISMS. 



the protoplasm of each being cut off by a septum, these 

 parts coalesce. A zygospore is thus formed from which a 

 new filamentous individual arises. 



Ascomycetse : Oidium Lactis (Fig. 39 B). This is a 

 common organism in sour milk and sour bread. It can easily 

 be cultivated on gelatine where the colonies appear to consist 

 of fine white filaments radiating from a centre. Micro- 

 scopically here and there the filaments (which may be 

 branched) are broken up, especially at the ends, into short 

 rod-shaped or oval segments often referred to as the oidia. 

 These behave like spores. Non-sexual reproduction also 

 takes place by the formation, within certain special cells in 

 the filament, of a definite number of spores to which the 

 special name of asci is applied. 



Perisporiaceae : (i) Aspergillus Niger (vide Fig. 39 C). 

 This, with other varieties of the same group is of frequent 

 occurrence, in especially vegetable putrefactions. It grows 

 readily in gelatine. It consists, to the naked eye, like the 

 other fungi described, of a mass of felted filaments which 

 microscopically are seen to form a septate branching 

 mycelium. Sexual reproduction does not take place, but 

 two forms of non-sexual reproduction occur, the variety 

 depending largely on the nutrition of the plant. The less 

 common form is effected by means of the formation of 

 structures known as perithecia. From a mycelial branch 

 a filament arises. At the end of this a swelling occurs, into 

 which the end of the filament penetrates and, twisting 

 upon itself, becomes detached and lies free in the proto- 

 plasm. This twisted part ultimately divides into a limited 

 number (not more than eight) of oval bodies, the asci or 

 spores, and, the surrounding protoplasm disappearing, the 

 latter lie free in the membrane. This ruptures and the asci 

 escape. After a period of rest these develop into new 

 individuals. The commonest method of reproduction is by 

 gonidium formation. Here a filament grows out, and at 

 its termination a club-shaped swelling is formed on which a 

 series of flask-shaped masses of protoplasm called sterig- 

 mata (vide Fig. 39 C6 ) are perched. At the free end of 



