CHAPTER II* 



MOLDS 

 FUNGI IN GENERAL 



Certain fungi commonly designated molds are constantly met in 

 microbiological studies. They are found as contaminating colonies in 

 microbial cultures. They are agents together with other microorgan- 

 isms in the processes of fermentation and decay in the soil, and in the 

 spoilage of food-stuffs. Certain of these forms approach the structure 

 and habits of other microorganisms very closely. Members of these 

 border groups have been sometimes described as bacteria, some- 

 times as fungi; among them the Actinomycetes have been principally 

 studied by bacteriologists, but recently Drechsler has succeeded in 

 describing their fruiting forms in terms which leave no doubt that 

 they are a fungous group. In describing microorganisms, cultural 

 reactions have been largely used in characterizing the bacteria and 

 related organisms; morphology has been the basis of nearly all descrip- 

 tions of the mycelial fungi. 



With some exceptions, there is, among the cells of the true fungi, 

 a differentiation of function into vegetative or assimilative cells and re- 

 productive cells. The fungous body is usually composed of threads 

 (technically called hypha, singular, hypha). These hyphce usually 

 branch in more or less complex manner forming networks or webs, 

 collectively called mycelium. Hyphae may be one-celled or composed of 

 many cells placed end to end as shown by the cross walls, called septa, 

 seen in them. These threads grow either by the formation of new cells 

 at the growing tips (called apical growth) or by the division of cells in 

 the hypha (intercalary growth). The fungous cells rarely divide in 

 three planes to produce solid masses of cells. Both vegetative and 

 reproductive masses are formed in great variety from such hyphae. 

 Often the thread-like character is almost or quite obliterated in the ripe 



* Prepared by Charles Thorn. A. Guilliermond has furnished the sections on " Cytology of 

 Molds " 



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