CHAPTER I.* 

 MOLDS. 



FUNGI IN GENERAL. 



A sharp line cannot be drawn between the bacteria and the fungi. 

 Certain border groups such as Leptothrix and Actinomyces, filamentous 

 forms in which branching and even the production of differentiated spores 

 occur, are sometimes described as bacteria and sometimes as fungi. 

 From the microscopic point of view, forms in which the cells can be 

 handled as bacteria by cover-glass staining may be conveniently treated 

 by bacteriologists. Forms in which the cells are larger, with definite 

 walls, vacuoles, and cell sap, in which the cells collapse when dried and 

 lose their distinguishing characters, may be better treated as fungi. No 

 rule holds for all groups. 



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 hypha 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 (inter- 

 calary 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 masses, which may be fleshy, woody, 

 carbonaceous, leathery and even horn-like in texture, as seen especially in 

 the mushrooms, bracket-fungi, etc., but even in such cases the early stages 

 show the structures to originate from masses of fungous threads. 



The formation of differentiated reproductive cells is, in general, 

 characteristic of the fungi. The method of reproduction presents great 



* Prepared by Charles Thorn. 



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