MOULDS. 389 



lace, giving rise to a felt or cotton-like growth known as 

 the mycelium. 



The individual filaments or threads which go to make _ 

 up the mycelium are known as mycelial threads or as 

 hyphce. While the bacterial cell is usually about 1 p. in 

 width the mycelial thread will vary from 2-5-7 y. in width. 

 In other words, the width of the mycelial thread is greater 

 than that of bacteria, and may be the same as that of the 

 yeasts. 



The threads may be very short, clinging to the surface 

 on which the growth is developing; or, they may be very 

 long, so that the resulting mycelium may have a height of 

 ^-1 inch or more. The color of the mycelium will vary ' 

 considerably in the different species. It may be pure white, 

 yellow, green, pink or black. 



Many of these organisms, especially the true moulds, 

 at a certain stage in their development give rise to repro- 

 ductive cells, and eventually spores or conidia form. 

 Usually a stalk or thread known as the fruit-hypha rises 

 upward and bears on its end the fruit organ. The latter is 

 so characteristic for the different groups or families that it 

 is utilized as the basis of a natural classification. It is 

 thus possible to divide the large group of moulds into well 

 defined genera and even species. In certain forms, inter- 

 mediate between the true moulds and the bacteria, the fruit 

 organs are wanting or are imperfect, and, in such cases, 

 the classification is based on general characteristics such 

 as habitat, size, cultural properties, etc! 



In general, the true moulds can be divided into two 

 groups according as the spores produced are contained in 

 a sac or sporangium, or are free and arranged in rows on 

 the ends of modified hyphas. 



A large number of families or groups of moulds are met 

 with accidentally in the ordinary routine bacteriological 

 work. The most important of these are the Mucor, Asper- 

 gillus, Penicillium and Oidium. 



