24 Proceedings 
general infection of the vineyards in the spring can be 
caused by the ascospores of the few perithecia produced ; 
and vinegrowers are still firmly of the opinion either that 
the mycelium hibernates in crevices of the bark or that 
the conidia are capable of living through the winter. 
We see, therefore, that there is reason for refusing off- 
hand to accept the statement that every year infection is 
always caused by ascospores, and we see, further, how 
valuable any definite knowledge on the subject would be. 
Now, by field-work, some light could, I think, surely be 
thrown on this problem. Every year in the Spring we see 
mildews re-appearing on their host-plants. There are 
several ways one could work at the solution of the problem. 
One might collect a great number of leaves on which 
perithecia occurred, in the autumn, and keep them wader 
natural conditions through the winter; then in spring, fix 
the fragments of dead leaves and their perithecia to the 
fresh living leaves of a host-plant, and watch if—and how 
—infection takes place. Or again, one might keep a sharp 
look out during the spring months for the f7s¢ appearance 
of mildew on leaves, and then under the microscope 
examine such leaves, and see if germinating ascospores are 
present, 
Now for the second question. Why do perithecia become 
reversed ? 
The phenomenon of the reversal of the perithecium takes 
place in two genera of the Z7ysiphacee—in Phyllactinia 
and Uncinula. In Phyllactinia, as the perithecium be- 
comes fully ripe, the spine-like appendages, which are bulb- 
ous at the base, turn downwards, so that the perithecium 
finally comes to stand on the points of its reflexed appen- 
dages. 
Now at this time a drop of mucilage is found on the 
apex of the perithecium. This drop of mucilage is pro- 
duced by the breaking down of the walls of certain peni- 
cillate cells, which are outgrowths from the apex of the 
perithecium, 
When the perithecium falls off from the leaf—which it 
readily does when the appendages are in the position shown 
