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THE ACTINOMYCETES, Vol. TI 



1. Straight, very little branching. 



2. Wavy, abundant branching. 

 II. Spirals formed. 



1. Spirals formed on the axis, irregu- 

 lar branching. 



2. Spirals formed on branches in clus- 

 ters. 



III. Verticils produced. 



1. Verticillate branches entangled like 

 a net. 



2. Verticillate branches formed on both 

 axis and branches, making primary 

 and secondary verticils. 



Okami (1952) grouped the genus Strepto- 

 myces on the basis of formation of aerial 

 mycelium into the following types: 

 I. Spirals not formed. 



1. Branches produced. 



2. Branches not produced. 

 II. Spirals formed. 



1. Spiral form mostly compact. 



2. Spiral form mostly loose. 



Shinobu (1958) criticized the systems of 

 Aiso and Okami on the basis that insufficient 

 attention was paid to the nature of the me- 

 dium. In the system of Aiso et al. the distinc- 

 tion between 1 and 2 of each type appeared 

 to him to be unclear, many forms belonging 

 to an intermediate type. Okami's system 

 was considered as incomplete because the 

 formation of verticils was not taken into 

 consideration. Waksman's system was be- 

 lieved to be comparatively better, but even 

 this system was criticized because cluster or 

 broom-shaped sporophore formation was not 

 considered as a sufficient characteristic, and 

 because a strain does not necessarily have 

 only one kind of spiral, but usually forms 

 various kinds of spirals which coexist (PI. II). 



Hesseltine et al. (1954) and Pridham et al. 

 (1958) considered the sporophore morphol- 

 ogy as reasonably stable under definite nu- 

 tritional requirements of the organisms. 

 Several morphological groups were sug- 

 gested. The components of each group were 

 considered as suggesting a logical natural 

 arrangement. The physiological data can be 



used to produce "species" or ''species- 

 groups," with morphology as a starting 

 point. Seven morphological sections were 

 created as subdivisions of the genus Strep- 

 tomyces. However, this system as well was 

 considered by Shinobu as having certain de- 

 fects because (a) culture media for morpho- 

 logical study were not examined thoroughly 

 enough; and (b) some of the sections may 

 often coexist in one strain. 



Shinobu (1958) emphasized the following 

 morphological properties of the aerial my- 

 celium : 



a. Outward appearance of mycelium 

 (powdery, cottony, leathery). 



b. Branching, especially the formation 

 and nature of verticils. 



c. Formation and nature of spirals. 



d. Formation and shape of spores. 



e. Thickness and length of mycelium. 

 Shinobu examined in detail the various 



properties of the aerial mycelium, emphasiz- 

 ing again the need for suitable synthetic 

 media. He concluded that the nature of the 

 aerial mycelium is one of the most important 

 characteristics for taxonomic study, but that 

 il should be considered in connection with 

 composition of the medium. The aerial my- 

 celium was classified into the following three 

 groups, from the standpoint of branching 

 and formation of spirals. 



Group I. Straight or wavy aerial my- 

 celium, monopodial branching, never pro- 

 ducing spirals or clusters. 



Group II. Spiral formation in the aerial 

 mycelium; long or short; loose or compact; 

 open or closed. 



Group III. Verticil or cluster formation 

 in the aerial mycelium. 



The loss of ability to form aerial mycelium 

 and sporogenous hyphae by certain Strepto- 

 myces cultures, on the one hand, and the 

 formation of aerial mycelium and sporo- 

 phores by certain species and strains of 

 Nocardia, on the other, led Bradley (1959) 

 to question the distinction between these 

 two genera. We have here simply another 



