MORPHOLOGY AND RELATIONSHIPS OF MICROORGANISMS 41 



threads called hyphce (sing, hypha). The whole mass of threads 

 or hyphse which go to make up the plant of the mold is called the 

 mycelium. In most molds certain threads are differentiated 

 for the production of spores. The mycelium of the mold may 

 extend over a considerable area, growing deep into the substratum 

 for food or into the air to develop spores. 



Histology and Structure of Molds. The mycelium in some 

 molds is continuous throughout its length, possessing no cross 

 walls which might separate the cells from each other. In the 

 majority of forms, and in all those of economic importance to 

 the veterinarian, the hyphee are divided by cross walls or septa 



Fig. 21. Mold hyphse: A, B, Xon-septate hyphse of the Phy corny cetes; C, 

 tip of a non-septate hypha, showing numerous nuclei and vacuoles; D, septate 

 branching hyphse; E, a single cell of a septate hypha, showing nucleus and vac- 

 uoles. 



(sing, septum). The cell wall is composed of true cellulose in 

 a few molds, in the majority it is chitinous as in the bacteria. 

 The almost universal presence of chitin in the cell walls of the 

 fungi is frequently lost sight of by those who regard its presence 

 in the cell walls of bacteria as evidence of animal affinities. The 

 protoplasm of molds, as in the yeasts, is made up of cytoplasm and 

 nucleus. The outer layer of the cytoplasm or ectoplast is readily 

 demonstrated in most molds by plasmolysis. In the forms that 

 do not have septa dividing the hyphse into cells, the numerous 

 nuclei are imbedded in the common cytoplasm. Functionally 

 each nucleus with its bit of surrounding cytoplasm constitutes a 



