1034 
Journal of Agricultural Research 
Vol. XXIV, No. 12 
colored onion scales. Occasionally there was a slight swelling of the 
spores (fig. 4). At Ph 3, about 43 per cent of the spores germinated, but 
the hyphae were abnormal in size and stunted, and in many cases the 
germ tubes ruptured. In the sterilized extract no germination occurred 
at Ph 1.6 to 2.2, except for an occasional ruptured germ tube at Ph 2.2. 
The growth of the fungus on onion decoction of various Ph values was 
tested. The medium was made as described above, except that 2 per 
cent dextrose was added. Duplicate portions of 75 cc. each in 300-cc. 
Jena glass flasks were used. The medium was inoculated by transferring 
a piece of stroma and mycelium from a potato agar culture of the organism 
to each flask. The flasks were kept in diffused light at room temperature 
(20° to 2 S^ C.) for 54 days. The mycelial growth was then removed 
from the remaining culture medium by filtration and the reaction of the 
filtrate determined. The Ph value of the medium before and after filtra- 
Ph/. 3 -4&hrs. 
Ph 3.0 
r'lG. 4. —spore germination of Colletotrichum circinans in onion scale decoction adjusted to the various 
degrees of acidity indicated. Note the ruptured germ tubes at Ph i.8 and 2.0, and the same together 
with swollen spores and short thick germ tubes at Ph 3. See further explanation in the text. 
tion, and at the end of the experiment, as well as the amount of fungus 
growth occurring in the flasks, are recorded in Table VII. 
A repetition of this experiment with Pyrex flasks and the use of spores 
instead of mycelium as inoculum yielded essentially the same results. 
It may be concluded from the above experiments that both the spores 
and the mycelium of Colletotrichum circinans germinate and grow well in 
onion decoction ranging in Ph value from about 3.5 to 8. As the actual 
acidity increases beyond 3.5 there is a sharp reduction in germination 
and growth, with a tendency toward rupturing of the germ tubes. It is 
important also to note that in the flask cultures, where good growth 
occurred, the reaction of the medium changed decidedly toward the 
alkaline during the period of the experiment. The rapidity of this change 
and the actual variations in the reaction from day to day were not 
determined. 
The acid toleration of the fungus having been studied, the reaction of 
the onion tissue was next considered. Plants of the Red, Yellow, and 
White Globe varieties growing out-of-doors were pulled at about 8.30 
