136 NON-PATHOGENIC MICRO-ORGANISMS. 



circumstances sexual reproduction occurs (vide Fig. 44 

 A i -3). Two filaments approach each other, and a small 

 piece of 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. 44 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. 

 Microscopically 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 reproduc- 

 tion also takes place by the formation, within certain 

 special sporangia in the filament called asci, of a definite 

 number of spores to which the special name of ascospores 

 is applied. 



Perisporiacese : (i) Aspergillus Niger (vide Fig. 44 C). 

 This, with other varieties of the same group is of fre- 

 quent occurrence, especially in 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. Though it is a matter of doubt whether sexual 

 reproduction takes place, two forms of reproduction occur, 

 the variety depending largely on the nutrition of the plant. 

 The less common form is effected by means of the for- 

 mation of structures known as perithecia, and it may 

 perhaps be that the perithecia owe their formation to a 

 sexual act. From a mycelial branch there arises a filament 

 (or hypha) which becomes specially coiled and transversely 

 septate at its end. From the base of the lowest coil of 

 the spiral two or three hyphse grow up towards its apex. 

 One of these being the first to reach the apex was regarded 

 by De Bary as a male organ. The others by branching 

 copiously produce a mass of closely woven hyphse which 

 form a closed wall to this structure, which is the perithecium 

 referred to. Within it numerous asci arise as the ultimate 



