PART II 



GENERAL BIOLOGY OF MICRO- 

 ORGANISMS 



CHAPTER VII 

 MORPHOLOGY AND CLASSIFICATION 



The minute living things included under the general term 

 microbe, are exceedingly various in form and structure as well as 

 in respect to food requirements and physiological activity. The 

 number of different microbes is so great and so great are the diffi- 

 culties involved in the accurate observation of their various 

 features, that the biological relationships of many of the various 

 forms to each other are not yet determined, and much of the 

 generic and specific terminology in common use rests upon insecure 

 foundation. Nevertheless a certain kind of order has developed 

 in our conceptions of the grouping of micro-organisms. 



Molds and Yeasts.^ — The molds are multicellular organisms 

 characterized by the formation of a network {mycelium) made up 

 of branching threads (hyphtB), and by their special fruiting organs. 

 These threads vary from 2 to 7/i in width. Within the group of 

 molds the structure of fruiting organs is used as the most important 

 character from which to determine relationships. The phycomy- 

 cetes, or algo-fungi, are characterized by the presence of sexual 

 reproduction in which the union of two cells gives rise to resting 

 cells, zygospores and oospores, which are enclosed in a thick wall. 

 The ascomycetes are characterized by a septate mycehum and 

 by the occurrence of a spore-sac called the ascus, which usually 

 contains eight spores but may contain a large number in some spe- 



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