76 BOTANICAL GAZETTE [january 



correlation is very evident in a comparison of types likt Actinomyces 

 II and XVI showing spiral sporogenous hyphae with a few wide 

 turns, and types hke IV, V, and XVII illustrating spirals of many 

 narrow turns. 



Rotation in the formation of spirals is specifically sinistrorse 

 or dextrorse in different species of the genus; and it is interesting 

 to note that here, as in the vegetable world in general, sinistrorse 

 are much more abundant than dextrorse species. Of the 1 7 species 

 with spiral sporogenous branches figured in the present paper, which 

 have been selected as representative of a much larger number, 5 are 

 dextrorse, 11 are sinistrorse, while the condition of the remaining 

 one could not be ascertained with certainty. In general, the pro- 

 portion appears throughout the entire genus. As a morphological 

 feature, the absolute constancy with which a species adheres to 

 one kind of rotation is noteworthy, particularly in view of the 

 extremely minute dimensions of the structures concerned. 



An examination and comparison of the relation of the sporoge- 

 nous branches to each other, and to the axial filaments, enables 

 one to recognize several tendencies, the distinguishing characteristics 

 of which are correlated with differences in the sequence of prolifera- 

 tion. Two main types may thus be recognized, approaching each 

 other in apparently intermediate forms, but moderately distinct at 

 the extremes: (i) an erect dendroidic type in which the sequence 

 of development of the sporogenous hyphae is successive; and 

 (2) a prostrate, racemose type in which the development is more 

 nearly simultaneous. 



In the erect type, well exemplified in Actinomyces I, the develop- 

 ment of the fructification starts from a single erect hypha with a 

 spiral termination. Sporogenesis commences at the tip by the 

 insertion of regularly spaced 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 its base, 

 and immediately below it the bud anlage of a new sporogenous 

 branch appears. As the latter is attaining its growth in length and 

 thickness, and its spiral disposition, the basipetal septation in the 

 axial filament proceeds to the septum above the insertion of this 

 first branch, the young spores thus delimited undergo maturation 



