CHAPTER V 



MORPHOLOGY AND CLASSIFICATION OF THE MOLDS 



Structurally the molds differ from the bacteria and the 

 yeasts in that they are multicellular, that is, the plant body 

 is more complex than that of bacteria or yeasts, and is made 

 up of numerous cells. Furthermore, the cells which make 

 up the plant body of a mold are not all uniform in size, 

 shape or function. Some are differentiated for purposes 

 of securing nutrients, others may be differentiated for pur^ 

 poses of reproduction. 



It should be emphasized that the molds as considered 

 here do not constitute a group recognized as such by the 

 botanist. All belong to the great class Fungi, but they 

 are scattered among several distinct subgroups. 



The plant body of the mold is made up of a mass of 

 threads, usually branched. This whole mass of threads 

 taken collectively, that is, the entire plant body, is termed 

 the mycelium. The individual threads are called hyphae. 

 In most molds the hyphae are of two principal types, those 

 which are differentiated for the purpose of producing 

 spores, called the fertile hyphae, and those which serve to 

 secure nutrients for growth, termed the vegetative hyphae. 



Structure of Mold Hyphae. — Two kinds of hyphae may 

 be recognized among the molds. In the first the cells of 

 the hyphae are separated from each other by definite cell 

 walls, that is, the threads consist of definite cells arranged 

 in chains, that is, cross walls are formed in the hyphae. A 

 cross wall is termed a septum, and the hyphae are said to 

 be septate. In the second group of molds the hyphae do 

 not usually show cross walls except during the process of 



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