286 PRINCIPLES OP SOIL MICROBIOLOGY 



monocellular mycelium, composed of hyphae, which show true branch- 

 ing, like that of higher fungi. The hyphae are rather long and 0.5 

 to 0.8/z in diameter (limits 0.3 to 1.2/j.). The mycelium develops 

 either in the substrate or on the surface, in the form of an aerial 

 growth. The aerial mycelium readily breaks up into short frag- 

 ments, which may look like bacterial rods and also resemble true bacteria 

 in their protoplasmic properties. When examined directly upon the 

 agar or in a hanging drop, or when properly fixed before staining, the 

 aerial mycelium will be found to consist of very fine, characteristic, 

 long or short branching hyphae with the distinct spore bearing 

 hyphae (only the closely related Mycobacteria may give a somewhat 

 similar picture). 



The spores, or reproductive conidia, are produced by a simultaneous 

 division of the protoplasm in the sporogenous hyphae, progressing from 

 the tip towards the base. They possess a greater power of resistance 



PLATE XVI 



Soil Actinomyces 



120. Cross section of a young Actinomyces "colony" upon agar, X 65 (from 

 Lieske). 



121. Spore germination and consecutive stages of mycelial development of an 

 Actinomyces (from Lieske). 



122. Young mycelium of an Actinomyces, growing 5 days at room temperature, 

 X 400 (from Lieske). 



123. Actinomyces (XIII), with a straight type mycelium; long mycelium, little 

 branching : a and b, long, unbranched hyphae, showing very slight spiral tendency ; 

 c, chain of spores; d, e, portions of aerial mycelium showing branching (from 

 Drechsler). 



124. Actinomyces griseus, with a short mycelium and abundant branching: 

 a, b, c, portions of aerial mycelium; d, e, spores germinating with one and two 

 germ tubes respectively (from Drechsler). 



125. Actinomyces reticuli, showing the formation of sporogenous hyphae in 

 knot-like groups: a, formation of septa in lower sporogenous branches; d, forma- 

 tion of secondary branches (from Waksman). 



126. Actinomyces (IX), showing the narrow closed fist type: a, b, portions of 

 aerial mycelium, the spiral termination of which are converted into chains of 

 uninucleated spores; c, portion of aerial mycelium with septa in axial filament 

 above insertions of some sporogenous branches; d, sporogenous branch; e, f, 

 germinating spores (from Drechsler). 



127. Actinomyces scabies, showing open spiral type: a, b, portions of aerial 

 mycelium, some lateral elements bearing secondary branches, developed suc- 

 cessively; c, successive stages in development of the sporogenous branch, c l x 

 and c l y representing either alternative or probably successive stages (from 

 Drechsler). 



