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BOTANY: C. DRECHSLER 
organism and several pathogenic types clinically similar to Act. bovis, revealed 
decidedly fungoid characteristics, not only in the profusely branched condition 
of the vegetative thallus when grown in culture, but also in the production of 
an aerial mycelium and Oidium-like spores, the view that the genus is to be 
placed with the Hyphomycetes has continued to receive support. 
According to another view which has gained quite wide acceptance, Actino- 
myces represents an intermediate group and a phylogenetic connection between 
the Bacteria and the Fungi. It is held that the genus originated either as the 
result of the development of bacterial forms possessing a tendency toward the 
branched condition, like the tubercle and the diphtheria organisms; or as the 
result of the reduction of hyphomycetous types, which, in their ultimate 
stages, yielded the much simpler true bacteria. 
In order to determine the merits of these contending views, the writer 
subjected a large number of saprophytic species isolated from the soil, air, 
etc., as well as several virulent strains of the potato scab organism secured 
from Mr. M. Shapavalov, to morphological study. The results may be 
summarized as follows: 
(1) The vegetative thallus of Actinomyces consists of a mycelium com- 
posed of profusely branching hyphae, the terminal growing portions of which 
are densely filled with protoplasm. Toward the center of the thallus, the 
vacuoles increase in size, and may be associated with the presence of meta- 
chromatic granules; the latter having nothing in common with bacterial 
endospores or 'micrococci,' for which they were mistaken by early observers. 
(2) The vegetative mycelium attains an extent incomparably greater than 
the branching figures recorded for bacteria of the acid-fast group; and the 
hyphae lack the uniformity in diameter generally characteristic of the 
Schizomycetes. 
(3) The aerial mycelium produced on suitable substrata by most species, 
occurs, usually, in the form of a mat of discrete fructifications; but in other 
species, these fructifications are frequently combined to form numerous pecul- 
iar erect Isaroid sporodochia. 
(4) In any case, each individual fructification represents a well characterized 
sporogerious apparatus, consisting of a sterile axial filament bearing branches 
in an open racemose, or dense capitate arrangement. The primary branches 
may function directly as sporogenous hyphae, or may proliferate branches of 
the second and of higher orders; sporogenesis, in the latter case, being confined 
to the terminal elements, the hyphal portions below points of attachment of 
branches remaining sterile. 
(5) Two tendencies in the development of fructifications are recognizable, 
one leading to an erect dendroidal type in which successively proliferated 
fertile elements undergo processes of sporogenesis in continuous sequence; and 
the other leading to a prostrate, racemose type, in which sporogenesis is de- 
layed in the older branches until the younger branches have also attained their 
