Frey—Physiology of Venturia Inequalis. 
333 
ing spores. The cavity may not be devoid of material as in some 
there is evidence of a gelatinous material which may take up 
water and swell thereby forcing out the spores. Whether an 
enzyme, or enzymes, are necessary to ripen the spores and digest 
the walls of the ascus is not known. Attempts to discharge spores 
by moistening and warming the perithecium after the spores ap¬ 
pear to be mature fails to produce a discharge, even if consid¬ 
erable pressure is applied. When the perithecium is wetted and 
then punctured with a needle, considerable discharge occurs. The 
conditions for discharge are, however, very complex. During 
May the asci contain mature spores but neither wetting nor heat¬ 
ing to room temperature would discharge the spores. July 6, 1917, 
leaves were obtained which had been lying on the sod and had not 
completely decayed. They contained perithecia full of asci and 
spores. The leaf was taken into the laboratory and placed in a 
moist chamber and a slide placed about an inch above the leaf. 
A tremendous discharge occurred. Several slides were then pre¬ 
pared and placed at various temperatures. About 80 per cent 
germination at 1-2° C. was obtained, but growth was extremely 
slow. At 2-3° C., 96 per cent germination was obtained. At 4° 
and 6° about the same per cent of germination resulted, but growth 
was more rapid. The optimum germination and growth occurred 
at 10-18° C. and then gradually decreased until 22° C. was reached 
when very little growth occurred, and the germination was greatly 
reduced. It may be well to state that the temperature control was 
only accurate to within a degree or more. The experiments con¬ 
ducted on spore discharge demonstrated rather conclusively that 
discharge of spores occurs only during rains or when the leaves 
are very wet, and that the discharge is greatest during the first 
two hours and gradually lessens. Temperature may influence the 
rate of discharge, but owing to lack of data at present it is not 
deemed possible to draw definite conclusions. 
The ascospores when first delimited appear round or lens¬ 
shaped. When mature they are two-celled and each ascus usually 
contains eight spores. Each cell has one nucleus which is no 
larger than the nucleus of one of the cells of the filament. The 
wall of the spore consists of two layers. With Heidenhain’s iron- 
alum haematoxylin the cytoplasm stains heavily, but the nucleus 
is much denser and more heavily stained. Evidently the proto¬ 
plasm also contains considerable food material. 
