LEAF-SPOT OF ALFALFA AND RED CLOVER. 7 
Under favorable conditions apothecia may reach 14 mm. in di- 
ameter, but are usually 1 mm. or less. Asci are 60 to 70 microns 
long, and about 10 microns in diameter. Paraphyses are slightly 
longer than the asci, nonseptate, and swollen at the ends. 
Ascospores of the two species (figs. 1 and 2) show slight differ- 
ences in size, those of Pseudopeziza trifoli being larger. The 
spores of each species have shown small variations in measurement 
when they were obtained under different conditions affecting their 
discharge. The most important of these variations has occurred 
when spores are obtained from apothecia which are drying rapidly. 
Under these conditions discharge is greatly accelerated, and the 
number of spores of smaller size is increased. Therefore, in order to 
obtain comparable measurements certain precautions were always 
taken to obtain spores of the same degree of maturity. Fruiting cul- 
tures of the fungus or leaves bearing apothecia were placed in the 
cover of a Petri dish over a layer of clear agar. After about 10 
hours, when the discharge be 
of spores was apparently 
proceeding at a uniform 
rate, the cover of the dish SS = 6) 
was turned about so that sie, 1—aAscospores of *Fic. 2.—Ascospores of 
the spores now fell on a new Pseudopeziza trifolii. Pseudopeziza medica- 
x 600. gints. X 600. 
portion of the agar surface. 
After half an hour a considerable number of spores were usually 
found on the agar. The cover was then removed from the dish, a 
small drop of water and a cover glass were placed on the area on 
which the spores were scattered,. and measurement was made as 
rapidly as possible. 
When a large number of spores have been measured to the nearest 
micron and the spore lengths arranged, as shown in Table IT, it has 
always been found that the number of spores of Pseudopeziza medi- 
caginis which measure 10 microns and less constitute more than 
half the total, while in the case of P. trifolit the number of spores 
which are 11 microns and longer constitute more than half the total. 
Table IL presents a typical comparison of the measurement of 100 
spores of each species. 
Taste I1.—Comparison of the lengths of 100 spores each of Pseudopeziza medi- 
cagmis and Pseudopeziza trifolii, measured to the nearest micron. 
Length (microns). 
Spores of— = 
Pseudopeziza medicaginis........... number... 7 26 33 24 LO) |eiayete a's ee |sfeimitiere 
Pseudopeziza trifolii...................- WOstersseeasis as 3 26 46 18 6 1 
