690 
Journal of Agricultural Research 
Vol. XXIII, No. 9 
MICROSCOPIC APPEARANCE 
The development of a culture of this organism is comparatively rapid. 
The conidia germinate almost immediately on the surface of a poured 
plate by the development of a germ tube about half the diameter of the 
spore itself (PI. 12, B). A cross wall is formed after the tube has grown 
in length to three or four times the diameter of the conidium, and pro¬ 
fuse branching occurs immediately afterward, together with continued 
growth in all directions from the conidium. The mycelium of this 
fungus is easily distinguished from that of other fungi commonly found 
as contaminations in a plate by its large diameter and its general robust 
appearance. Its contents are distinctly granular and vacuoles are rare 
except in old cultures. Anastomosing of hyphae is frequent. It may 
occur between two hyphae which have arisen from the same spore or 
between two adjacent hyphae from different spores. Plate 13, I and J, 
are camera-lucida drawings showing anastomosis. The conidiophores 
may be distinguished in a young culture very early in their development. 
They arise perpendicularly from a cell of a horizontally growing vegetative 
hypha, becoming larger and olivaceous in color a short distance above 
the surface. Plate 12, D, is a drawing of the base of a conidiophore, 
showing its attachment to the vegetative hypha. Sometimes a single 
cluster of conidia is produced on the end of such a conidiophore. More 
frequently, however, the tip will divide and two equal branches will 
continue the growth. Often these will divide again, and a third or even 
a fourth division may occur, always dichotomous, the internodes becom¬ 
ing shorter by about half with each subsequent division. Finally the 
conidial head starts to form, this too by continued dichotomous divisions 
of the tip (PI. 12, A). It was difficult at first for the writer to determine 
clearly the definite mode of attachment of the conidia to the ultimate 
branch tips of the conidiophore. Finally, by studying the development 
of very young cultures, this point was made clear. The conidia are borne 
on very fine attenuations of the ultimate tips of the conidiophore, these 
final cells being very turgid though thin-walled and fragile. No wall was 
discernible. Plate 12, C, depicts immature conidia attached to the 
conidiophore. Upon the maturity of the conidia, or upon the forcible 
detachment of nearly mature conidia, the ultimate cells of the conidio¬ 
phore collapse and hang in a shapeless mass on the end of the next 
branch back, this tip becoming rounded out meanwhile, owing to the 
turgidity of the cell. It was impossible to see on a mature fruiting branch 
the exact connection of a mature conidium, owing to the density of the 
cluster of conidia. 
Microconidia are formed in abundance, beginning after the cultures 
are about 10 days old. The writer never observed them in nature. Media 
favorable to heavy conidium production, such as corn meal or potato 
agar, sometimes do not readily produce microconidia. Upon media 
which do not produce conidia abundantly, such as oatmeal agar, 
cooked potato plug, and boiled rice, the microspores may often more 
readily be found. The writer has observed that they may often be 
found upon the thin piece of medium which has carried the transfer from 
one plate or tube to another. Microconidia are extremely small, from 2 
to 3 n in diameter. The manner of production was readily observed, 
however, by examining the exposed surface of a poured plate, with 
0.5-mm. water immersion objective. Considerable variation was notice¬ 
able in the type of conidiophore on which they were borne. Perhaps the 
