May 10,1924 Botryosphaeria and Physalospora on Currant and Apple 597 
Micropycnospores are found in culture and nature associated with the macro- 
pycnospores of both the Sphaeropsis and Dothiorella types. They may occur 
in separate locules or be intermingled with the macropycnospores. They are 
minute in size, about 2-3 m long, oblong, and have never been observed to germi¬ 
nate. See Plate 2, figure N. 
An interesting and apparently constant difference between the ascospores of 
the two fungi is found in their method of germination. Ascospores of Botry¬ 
osphaeria ribis, whether from currant or from apple, characteristically develop 
two germ tubes which branch before they have reached more than 8 or 10 times 
(PI. 2 O. and P.) the length of the spore. Even where only one germ tube is 
produced it usually branches while rather short. Ascospores of Physalospora 
malorum, on the other hand, usually develop only one germ tube which rarely if 
ever branches before it reaches a length equal to 50 or 60 times that of the spore 
itself. (PI. 2, Q. and R .) So constant under the conditions of our work was 
this apparently trivial character that in the case of two hundred eighty-six 
ascospores of these two fungi in which the type of germination has been observed 
and the development of the pycnospores in pure culture subsequently obtained, 
those ascospores which germinated by means of a single, long, unbranched germ 
tube have always produced pycnospores of the Sphaeropsis type and those 
which germinated by means of the shorter branched germ tubes, usually two to 
a spore, have always produced pycnospores of the Dothiorella type. 
On many culture media early stages of the development of the two fungi 
appear much alike, especially when grown in dry air at temperatures above 
22° C. They may be readily distinguished, however, on beef agar made accord¬ 
ing to the following formula: 
Add 3 gm. of beef extract, 10 gm. peptone, and 5 gm. of sodium chlorid to 
one liter of distilled water. Steam one hour; titrate with hydrochloric acid and 
make up to plus 10, Fuller’s scale. Add enough water to make one liter, and 
li per cent shredded agar. Steam one hour. After cooling to 60° C. add the 
whites of two eggs well beaten—steam another hour, filter through cotton, tube 
and autoclave 20 minutes at 15 pounds pressure. 
Cultures made on agar slants of this medium from mycelial transfers show 
after ten days a loose felt of short, rather fluffy mycelium on the surface of the 
medium. Botryosphaeria ribis , however, leaves the color of the medium un¬ 
changed (Baryta yellow) (7) whereas Physalospora malorum changes the medium 
to a dark color, between mummy brown and black. 
Cultures on corn meal in 100 cc. Erlenmeyer flasks which have reached the 
stage of producing mature pycnospores are readily distinguished by the surface 
character of the fungus growth. Fruiting or nearly mature cultures of Botryo¬ 
sphaeria ribis show numerous raised knob-like stromatic bodies usually 2 to 3 
mm. wide and 3 to 4 mm. high in which the pycnidia are contained. (PI. 1, E.) 
Fruiting cultures of Physalospora malorum on corn meal in flasks on the other 
hand have a much more uniform surface without prominent regular elevations 
of any kind, the pycnidia being almost completely buried in the mycelial growth. 
(PL 1, F .) 
If the various differences in stromata, size of ascospore, method of germina¬ 
tion, cultural characters, and different pycnidial stages mentioned above are 
constant, they furnish a good basis for generic segregation. The two generic 
names which have commonly been applied to the two species on these hosts 
are here used for convenience and clearness. 
SUMMARY 
The life histories of Botryosphaeria ribis, causing cane blight of currant, and 
Physalospora malorum, causing black rot of apple, have been verified repeatedly 
by the development of the pycnospores from single ascospores in pure culture. 
The methods by which pycnospores of these fungi were readily produced in 
pure culture are briefly described. 
