CHAPTER XX 

 ACTINOMYCETEAE 



The systematic position of this group of organisms has long been ques- 

 tioned. Since the mycelium is usually much more slender than that of other 

 groups of fungi and the arthrospores are often bacilliform and of approxi- 

 mately the same magnitudes as bacteria, many bacterial systematists have 

 included this order in the Schizomycetes, often adding Mycobacterium and 

 Corynehacterium to the group. On the other hand, mycologists who have 

 had occasion to work with the group (Bary, Thaxter, Sauvageau & Radais, 

 Gasperini, Drechsler) have always included them in the Fungi Imperfecti 

 along Avith the Hyphomycetes. The arguments of the bacteriologists have 

 usually been based on the staining reactions, development of elavate elements 

 in the animal body with Actinomyces, representing either the primitive stage 

 from which Mycobacterium and Corynel>acterium form degeneration stages or 

 the culmination from increased production of mycelium. Witter (1933) points 

 out that he was unable to find either chitin or a definite nucleus in the species 

 he studied. 



On the other hand, the mycologists have held that the spore production 

 of Actinomyces is essentially similar to that of the conidial production of the 

 imperfect fungi, which has nothing in common with bacterial structures, and 

 that many of the apparent resemblances are the result of careless technic. 

 Drechsler (1919) has perhaps given the most careful attention to the mor- 

 phology of the group, and we owe much of our knowledge of the group to 

 his work. It is to be regretted that his subsequent duties in the Department 

 of Agriculture have prevented his continuing the study of this group and 

 that he has been unable to turn his rich experience in the morphology of the 

 group to the presentation of a systematic account. Only one who has worked 

 Avith the group from the standpoint of its morphology for a considerable time 

 is really competent to evaluate the conflicting accounts in the literature and 

 to make the necessary assumptions and correlations in filling the lacunae of 

 imperfect descriptions. In the following account, the material is frankly a 

 compilation of the literature, in the hope that this may lead to a keener 

 realization of the lacunae in our present knowledge. 



The mycelium of Actinomyces has very slender filaments, commonly 0.2- 

 1.0/i, in diameter, rarely up to about 1.5/a. It is generally sparsely and irregu- 

 larly septate, occasionally somewhat regularly septate, but even then less so 

 than in the other Fungi Imperfecti. Branching is common, probably never 

 truly dichotomous, although in a few species it is impossible to be certain. 

 Usually a lateral bud develops at some distance back of the growing tip and 



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