Actinomvcctcs 77 



green and creani-coloied, ne\er distinctl)' yellow, red, or orange, as 

 the first two genera are; three species were described. 



According to Krzemieniewska, Cyf. hiitcJiinsoni is a totally differ- 

 ent species from Sp. cytojjJiaga, since the former docs not form 

 microcysts and the latter does. Spirochaeta cytophaga is believed 

 to be quite distinct from other species of Cytophaga in its life cycle, 

 which resembles more closely that of the Myxococcus of the myxo- 

 bacteria. The name Cyt. myxococcoides was suggested for this or- 

 ganism. Germination of the microcysts and their transformation into 

 rods are influenced by the reaction of the medium, temperature, and 

 oxygen tension. Similar results concerning the life cycle of this 

 organism were obtained by Issatchenko, who suggested, however, 

 that the name given by Winogradsky be reserved for the organism. 

 Another organism belonging to this group was described by Rippel 

 under the name Itersonia fcrriiginea. Under certain conditions, the 

 cellulose bacteria are adapted to a specific mode of nutrition, as 

 shown for the organisms found in rice fields or iron-rich soils; these 

 bacteria require a certain amount of iron to make their optimum 

 growth. Their optimum pH is 8.0; growth ceases at pH 4.5 even 

 in presence of sufficient iron. 



Other Bacteria. Many other groups of bacteria are found abun- 

 dantly in the soil. Among these are mycobacteria, corynebacteria, 

 \arious anaerobic bacteria in addition to those listed above, and a 

 host of other bacteria characterized by specific physiological or mor- 

 phological properties. Some of them are adapted to a special mode 

 of nutrition and may possess various biochemical properties which 

 render them of great economic importance. These include the nitro- 

 gen-fixing bacteria, which are treated in detail elsewhere (p. 191); 

 antibiotic-producing bacteria, like B. subtilis, B. brevis, and B. 

 polymyxa; bacteria capable of decomposing the capsular material of 

 the pneumococcus and of oxidizing p-aminobenzoic acid and an- 

 thranilic acid; and various coliform bacteria. 



ACTINOMYCETES 



Actinomycetes form, taxonomically, a link between the bacteria, 

 tlirough the genera Mycobacterium and Conjnebacterhim, and the 

 true fungi. They are characterized by the formation of a unicellu- 

 lar mycelium, composed of hyphae, which show true branching, 

 similar to that of fungi. The hyphae are rather long and are usually 



