78 BOTANICAL GAZETTE [january 



In addition, however, to species in which these two types are 

 clearly distinguished, a still larger number of species present a 

 combination of the two features. Frequently the open racemose 

 arrangement of the lateral branches on the main axial filament is 

 associated with a successive order of development in the further 

 ramifications of the branches (figs. 63, 79). The presence of a 

 septum above the insertion of a branch is characteristic of more 

 species than is its absence (figs. 2, 5c); and in some species both 

 conditions prevail (figs. 53, 79, 81). In other forms a fructifica- 

 tion with successive development may terminate a long prostrate 

 filament. 



In a few species, particularly Actinomyces X and XVIII, there 

 are formed, in addition to the more regular fructifications, others 

 of a more miscellaneous tendency. The branching axial filaments 

 are relatively thick, densely filled with protoplasm, and bear at 

 very close and irregular intervals a short, thick, unbranched spo- 

 rogenous hypha with Httle or no spiral modification (fig. 103). It 

 seems quite probable that this type of development is associated 

 with the excessively rapid growth that characterizes the two forms 

 in which it was most frequently observed. 



The degree of completeness to which the aerial mycelium of 

 Actinomyces is converted into spores has generally been overesti- 

 mated. On the contrary, sporulation is quite strictly confined to 

 terminal elements, never as a rule passing beyond the first junction 

 with another element. The proliferation of the branch nearest the 

 end of the axial filament limits spore production in this filament to 

 the portion beyond the insertion of the branch; and in the same 

 manner the proliferation of a secondary from a primary lateral 

 branch results in a sterilization of the portion of hypha below the 

 insertion of the new branch. In one species, Actinomyces V, sporu- 

 lation is even further restricted by the apparent abortion of a 

 number of potential spores at the proximal end of the unbranched 

 lateral branches. The hyphal portion involved first develops as 

 usual, but when the characteristic septation associated with the 

 delimitation of spores in this species appears in the spiral, it is not 

 extended to the base of the branch, although indications of regu- 

 larly spaced membranes may usually be distinguished (figs. 21, 



