MEDICAL MYCOLOGY 



CHAPTER I 

 GENERAL MORPHOLOGY OF FUNGI 



The Fungi form a large heterogeneous group of plants, including all those 

 lacking chlorophyll, which are not closely nor obviously related to other groups. 

 In a few primitive families, the vegetative body is naked and amoeboid. In 

 the rest of the fungi, it is surrounded by cell walls and usually appears as 

 septate filaments, called hyphae. The vegetative hyphae are collectively 

 known as mycelium. Under certain conditions of nutrition, as in solutions 

 of very high or of very low osmotic pressure, the hypha grows by sprouting, 

 when a small protuberance enlarges, rounds off and is abjointed (cut off by 

 a septum) from the mother cell. The daughter cell, called sprout cell or 

 blastospore, continues to increase in size and eventually separates from the 

 original group of cells. In certain groups, as in the yeasts, no other type of 

 vegetative body is known. When conditions for growth are unfavorable, the 

 protoplasm contracts, rounds up and secretes a special thick wall, forming 

 resting cells, called hypnospores or chlamydospores. (Fig. 1.) With the re- 

 turn of favorable environmental conditions, these hypnospores again develop 

 normal vegetative mycelium. 



In a few groups of fungi, the hyphal wall gives the cellulose reaction, in 

 most others that of chitin. In fructifications and resting cells, the hyphal 

 wall first appears as a thin, hyaline membrane which becomes thicker and 

 may be further differentiated by secretions and deposits of minerals or resins, 

 or colored by pigments. A relation between the fundaments of the wall and 

 mitosis has been demonstrated in only a few cases, as in ascospore formation. 

 In general, the wall is gradually differentiated from the cytoplasm without 

 nuclear aid. The septum often forms by furrowing (annular thickening of 

 the walls, like an iris diaphragm in a camera) . For the maintenance of inter- 

 cellular communication, the septa are frequently pierced by a few openings 

 through which pass protoplasmic threads. 



During rapid growth, there may be a delay in the formation of septa, 

 later compensated by simultaneous or successive development of septa. In the 

 Phycomycetes, the septa are wholly suppressed ; the whole mycelium is then 

 a single, branched, multinuclear mass of filaments, becoming septate during 

 the formation of reproductive organs, or during conditions of poor nutrition 

 or of senescence. 



The individual hyphae generally are intertwined in feltlike masses. Such 

 a group of hyphae, called the mycelium, usually absorbs food at any point 



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