ACTINOMYCETEAE 697 



to one in which the helix is so strongly compressed that its adjacent turns are 

 in continuous contact, is usually delayed until the later growth in thickness 

 by the sporogenous filament. Specific differences may not only be indicated 

 by the obliquity of the helix, but involve also the number and diameter of its 

 turns and its construction with reference to a dextrorse or sinistrorse condi- 

 tion. The range in different species extends from two or three turns in 

 Actinomyces II (Fig. 112) to over twenty turns in others, the range in an 

 individual species being much smaller. Coils of over twelve turns are very 

 rare. The diameter of the helix is more or less inversely proportional to the 

 number of turns characteristic of the species. 



Rotation in the formation of the helix is specifically sinistrorse or dex- 

 trorse in different species, the sinistrorse condition being the more common 

 as is general in plants. For a given species the condition of rotation of the 

 helix is constant. 



Two main types of branching of sporogenous filaments from the main 

 axis are evident ; the erect or dendroid type, in which the sporogenous hyphae 

 are successively developed, and the prostrate racemose type, in which develop- 

 ment is more or less simultaneous. In the erect type, the development of the 

 fructification starts from a single erect hypha with a helical termination. 

 Sporogenesis starts at the tip by the insertion of regularly placed septa and 

 proceeds downward toward the base of the filament. Usually, before much 

 of the hypha has been involved, a single septum will appear well toward this 

 base, and immediately below it a bud of a new sporogenous hypha appears. 

 As the latter is attaining its growth in length and thickness and its helical 

 disposition, the basipetal septation in the axial filament proceeds to the septum 

 above the insertion of this first branch, the young spores thus delimited un- 

 dergo maturation processes, the helix becomes relaxed and the chain of spores 

 subject to disruption. The branch now passes through the same stages of 

 development as the axial hypha and in turn gives rise to a sporogenous branch 

 below a septum a little above its own insertion. The number of sporogenous 

 branches developed below a single septum is generally increased by subse- 

 quent proliferations, and the initiation and development of successive orders 

 may be indefinitely repeated. Complex fructifications are frequently developed 

 in which a succession of the processes described are occurring simultaneously 

 at many points. 



In the second type, there is no such clearly defined relation between 

 younger and more mature sporogenous hyphae. Development of a fructifica- 

 tion is initiated by the proliferation of branches at irregular intervals on the 

 distal portion of a prostrate axial filament which often exceeds 1 mm. in length 

 (Fig. 113). The branches may either cease their more extensive development 

 after forming a helix or themselves proliferate a secondary branch a short 

 distance above their own insertion, and this in turn may form a helix and 

 give rise to a tertiary branch. By repetition of this process, each lateral ele- 



