276 
AIycologia 
the spore cell, one originates a few mikrons beyond the spore wall, 
giving in the majority of cases a growth with pronounced decus- 
sating branches (plate 99, figs. 1-5). 
Tests of the comparative rate of growth of pycnospores and 
ascospores were first made at 22° C., but it was found by later 
work that 25° C. gave a more pronounced difference. Camera 
lucida drawings were made at hourly intervals for the ascospores 
after the first eight hours and at intervals of two hours for the 
pycnospores. At the end of eight hours the ascospores produced 
a strong hypha from each cell, while the pycnospore had not yet 
swollen to its full size ; after 22 hours the pycnospore had pro- 
duced a short unbranched hypha with little or no septation, while 
the ascospore had produced a much branched linear aggregate of 
cells (plate 100). The series of drawings shown will serve to 
emphasize the pronounced difference in the growth from the 
pycnospores and ascospores. 
Plate Cultures 
The marked difference in the rate of growth from pycnospores 
and ascospores suggested the strong probability of being able to 
differentiate the two types of colonies in plate cultures by the 
size of the colonies at the end of a certain time. Various culture 
media were tried but 3 per cent, dextrose agar, plus 10, again 
appeared to be the most suitable. The poured plates were made 
in the usual manner from spores obtained in the same way as for 
the hanging-block cultures, and practically pure cultures of the 
blight fungus were always obtained. The cultures were held at 
a constant temperature of 25° C. All of the tests made showed 
that ascospore colonies became visible and conspicuous when the 
pycnospore colonies were still minute and invisible to the naked 
eye. At the end of three days’ time, colonies originating from 
ascospores were 0.5-3 •'“'‘ri''- diameter, the size depending upon 
the crowding in the plate, while those originating from pycno- 
spores were not visible to the naked eye (plate loi) ; after four 
days of growth the ascospore colonies were 1-4 mm. in diameter 
while the pycnospore colonies showed an average diameter of 
400^. The time of appearance of the yellow centers in the colo- 
