May 10,1924 
Physalospora malorum on Currant 
585 
single ascospore culture from this material all produced pycnospores indistin¬ 
guishable from those of Sphaeropsis malorum. Subsequent investigation showed 
the fungus to be apparently identical with Physalospora malorum. The specimen 
here discussed has been deposited in the pathological collections of the Bureau of 
Plant Industry, United States Department of Agriculture. 
COMPARISON OF THE PHYSALOSPORA FROM CURRANT AND 
FROM APPLE 
The first characteristic which suggested that the material in question was re¬ 
lated to Physalospora rather than Botryosphaeria was that the ascospores ger¬ 
minated by the single long unbranched germ tube characteristic of Physalospora 
and never, in the writer's experience, found in B. ribis. In cultural characters 
this fungus also agreed with cultures of P. malorum from apple on all the media 
tested and was readily distinguishable from B. ribis on such media as beef agar, 
potato agar, and corn meal in flasks. 
The comparative size and shape of the spores from the two hosts is shown in 
Table I. The ascospores measured were taken direct from the host. The 
pycnospores, on the other hand, were grown in pure culture from single asco¬ 
spores, as this seems to be the only method of making sure of the actual connec¬ 
tion of the two spore forms. The close similarity in size and shape of the spores 
from the two hosts is apparent This agreement is more marked in the case of 
the pycnospores, which were grown in pure culture under similar conditions, 
than in the case of the ascospores which were taken from the hosts. Whether 
this circumstance is significant and indicates either that the size of the ascospores 
is slightly modified by the host, as suggested by Paddock for the pycnospores, 
or that the form found on currant is actually slightly different from that on 
apple can not now be determined. This point could be settled only by the 
production of ascospores in quantity in pure cultures, or on the host under sterile 
conditions. Neither of these lines of attack is possible with our present knowl¬ 
edge. 
Table I.— Spores of Physalospora malorum 
ARRANGED BY CLASSES ACCORDING TO LENGTH 
Length (microns) 
Total 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 
Ascospores on apple_ 
223 
1 
1 
5 
8 
4 
11 
10 
16 
11 
31 
20 
28 
24 
30 
11 
6 
3 
2 
1 
Ascospores on currant- 
Pycnospores in culture 
146 
- 
1 
- 
4 
8 
9 
15 
9 
30 
15 
12 
21 
4 
6 
6 
3 
2 
- 
- 
1 
-- 
from ascospores on 
3pp|p 
100 
j 
5 
1 
18 
17 
14 
20 
11 
9 
3 
1 
Pycnospores in culture 
from ascospores on cur¬ 
rent. 
100 
1 
1 
13 
5 
14 
1 
13 
16 
11 
15 
5 
1 
3 
1 
1 
ARRANGED BY CLASSES ACCORDING TO WIDTH 
Width (microns) 
Total 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
A ^oospores apple. 
223 
25 
31 
46 
68 
26 
23 
3 
1 
Ascospores on currant 
146 
1 
2 
14 
23 
41 
33 
22 
9 
1 
Pycnospores in culture from asco- 
spnres nn apple 
100 
4 
8 
36 
25 
17 
8 
2 
Pycnospores in culture from asco- 
<?pores on currant ___ 
100 
6 
8 
36 
30 
11 
5 
2 
3 
96036—24t-8 
