482 
Journal of Agricultural Research 
Vol. XI, No. 10 
Fig. 4. —Diaporthe phaseolorum: Ger¬ 
minating pycnospores. X500. 
Under favorable conditions, such as in a nutrient broth or beef agar, 
the pycnospores germinate in about six to eight hours at room temper¬ 
ature. Previous to germination the spores 
become almost spherical and slightly en¬ 
larged. Usually but one germ tube develops, 
but occasionally two (fig. 4). One or both 
of the oil globules may disappear at this 
stage or remain until the germ tube is several 
times the length of the spore. Growth is 
rather slow at first, the hyphal growth attain¬ 
ing a length compared with the diameter 
of the spores as shown in figure 4 in 48 
hours. During this time branching may oc¬ 
cur, and septa rarely are formed till later. 
The bodies called stylospores are frequently 
found either alone or accompanying the 
pycnospores in pycnidia on the pods. They 
have never been found on the leaves. 
They are long, slender, hyalin, nonseptate, straight or curved bodies 
(fig. 5) borne on short, rather stout awl- 
shaped simple hyalin stylosporophores (fig. 
6). Figure 5 shows some stylosporo¬ 
phores with stylospores attached. They 
are produced but sparingly the early part 
of the season or when the pycnospores 
are most abundant. As the season advances 
the stylospores increase in number and 
appear to be associated, though not always, 
with a saprophytic existence. Following 
the death of the host and the gradual 
disappearance of the pycnospores the stylo¬ 
spores increase and finally become very 
numerous. Specimens which bore practically no stylospores in the fall 
bore them in increasing numbers throughout 
the winter. There is a possibility from the 
data at hand that the stylospores may be 
associated with a lack of food supply. They 
are produced in some culture media freely, 
but not until after the food supply becomes 
more or less exhausted. Although in cultures 
Fig. 6 —Diaporthe phaseolorum: a the pycnospores are usually exuded from the 
group of stylosporophores. X500. 
beak m seven days, the stylospores have never 
appeared sooner than u and generally not before 15 to 30 days after inocu¬ 
lation. The average size of the winter crop of stylospores developed 
Fig. 5. —Diaporthe phaseolorum: Styl¬ 
osporophores. (a) The stylosporo- 
phore is attached to the stylospore. 
(6) Stylospore not, attached to the 
stylosporophore. X500. 
