168 MICRO-ORGANISMS AND FERMENTATION. 



vegetative and reproductive organs of the fungus pass through. 

 We shall return to this subject when we come to a description 

 of yeasts. The cells form the mycelium of the fungus. This 

 is composed of branched or unbranched threads (Hyphse), 

 usually provided with transverse walls, the growing region 

 being always at the apex. Outgrowths may arise from the 

 older cells which develop to form lateral branches. Trans- 

 verse cell-walls are usually absent in the mycelium of fungi 

 belonging to the Mucor spores. Thus, the whole of the vege- 

 tative portion of the mycelium of these fungi, with its intricate 

 network of branches, consists of one single cell. Amongst 

 the members of this genus a second form is known. Under 

 special conditions, the submerged portion of the mycelium 

 divides into separate cells, which break away from each other, 

 become rounded off, and then give rise to protuberances which 

 themselves repeat a similar mode of growth. This is the 

 so-called spherical yeast, which grows in the same way as 

 true yeast. The same modification has been found to occur 

 amongst many other forms of moulds, and there exist, more- 

 over, forms exhibiting every intermediate stage down to those 

 in which the mycelium is almost entirely suppressed, and 

 the greater part of the growth takes the form of budding. 



Many moulds form peculiar resting organs, in which the 

 walls are thickened and the mycelia closely packed together, 

 surrounded by a dark, sometimes felted, pseudo-cortex formed 

 by the outer hyphae. In this way the small hard bodies, known 

 as Sclerotia, are formed. These are packed with stores of 

 reserve food material, and may retain their vitality throughout 

 a lengthened period, thus serving to ensure the maintenance of 

 the species during conditions which are unfavourable to growth. 

 Passing on to the manner of reproduction of the moulds, we 

 are brought face to face with the remarkable fact that these 

 organisms, although occupying so low a position in the vege- 

 table kingdom, possess in many cases, not one only, but several 

 entirely different methods of reproduction. Every stage of 

 complexity may be met with, from the simplest forms of re- 

 productive organs to the most highly developed. In Oidium 

 lactis reproduction is effected without the aid of any special- 

 ised organs. The threads of the mycelium divide quite simply 



