ENnpDoTHia CANKER OF CHESTNUT 567 
nuclei then being present. The nuclei pass out into the germ tubes 
almost as soon as they start. The wall, also, has increased in thickness 
until it almost equals the diameter of the resting spore. 
Germination of ascospores 
Unlike the pycnospores, the ascospores germinate readily in pure water. 
They do not require a period of rest, but germinate directly after maturity 
if placed under proper conditions. The time required for the process 
to begin after the ascospores are placed in water is much shorter than for 
pycnospores, being about six to twelve hours at room temperature. In 
regard to the effect of temperature on germination, Fulton (1912:52) 
says: “‘ Ascospores germinate best at a temperature of about 70° F., 
but a good percentage of germination occurs at 85° and 45° F. Even 
at 38° F. the germination of ascospores was 25 per cent in the first twenty- 
four hours and reached 70 per cent in three days.”’ 
Like the pycnospores, the ascospores swell before germination, but not 
to so great an extent. The first germ tube usually appears at the end — 
only occasionally being lateral; the next one comes from the other cell; 
and these are followed by a second one from each of the cells, making a 
total of four germ tubes. Their order of appearance, size, and manner of 
septation and branching are best understood by reference to the draw- 
ings of successive stages in Fig. 91. The germ tubes from the ascospores 
grow much more vigorously than do those from the pycnospores. By 
sowing ascospores on chestnut-bark agar, mature pycnidia have been 
produced in five days. 
Vitality and longevity of the spores 
Pycnospores.— Reasoning from analogy with what is known of the 
vegetative spores of many other fungi, one would not expect the pycno- 
spores to survive winter conditions; but the fact is quite the contrary. 
During each month of the winter of 1912-1913, spores were collected in 
the woods from spore horns, from pycnidia imbedded in the stromata, 
and from superficial pycnidia on wood, and in every test more than fifty 
per cent of the spores germinated. It appears, then, that winter condi- 
tions have very little effect on the viability of the pycnospores. Heald 
and Gardner (1913 a) also find that pycnospores can be subjected to 
freezing temperatures for considerable periods without losing their 
viability. 
The longevity of the conidia varies greatly with the way in which they 
are kept. Spore horns collected and kept dry in the laboratory and 
tested each month for germination showed very little diminution in the 
percentage of viable spores at the end of one year. On the other hand, 
when the spore-horns were dissolved in water and the water was allowed 
