AECIDIOSPORE DISCHARGE AS RELATED TO THE 
CHARACTER OF THE SPORE WALL 1 
By B. O. Dodge 
Pathologist, Fruit-Disease Investigations, Bureau of Plant Industry, United States 
Department of Agriculture 
During the prosecution of cytological studies on species of rust, the 
writer has made some observations on the development of their aecidia 
and on the origin and discharge of aecidiospores. The formation of 
germ pores and the concomitant development of structures which play 
an important role in spore discharge from the aecidium of Gymnospor- 
angium myricatum (Schw.) Fromme are briefly described in this paper. 
Attention is also directed to important differences obtaining with respect 
to these features in the orange-rusts of Rubus. 
The mechanics involved in the discharge of spores by such fungi as 
Pilobolus have always been a fascinating subject for investigation. 
More recently Buffer (r) 2 has added greatly to our knowledge of spore 
discharge by the Hymenomycetes, and has pointed out that in the com¬ 
mon mushroom there is a very delicate adjustment of organs to insure the 
unobstructed fall of the spores between the gills as they come to maturity. 
The basidiospore is started off along its sporabolic trajectory with an 
initial horizontal velocity imparted it by the force of some miniature 
explosion, as it were. The actual mechanics of the process stiff remain 
a mystery. It is a well-known fact that the sporidia of Gymnosporan- 
gium are frequently set free from the promycelium with enough force to 
carry them well beyond the other promycelia on the telial horns. 
Dietel (j) has shown by measurements that sporidia of certain rusts are 
discharged from sterigmata with sufficient violence to carry them out 
horizontally nearly a millimeter. 
Observations that have been made on the part played by the peristomal 
teeth of moss capsules or by the segments of the “peridium” of the 
Geasters in spore discharge have probably led us to assume that the 
hygroscopic action of peridial cells of the*roestelia type serves as much 
to check the scattering of spores during unfavorable weather as it does 
to dislodge them. • 
In attempting to make stereoscopic photographs of the beautiful 
aecidia of G. myricatum with a binocular outfit, the writer (5) was not 
very successful in obtaining clear pictures of the spores in the cups, 
because the group of spores brought into focus generally disappeared 
before the completion of the exposure. On examining aecidia on freshly 
gathered leaves with a microscope of fairly low power, it was noticed 
that the spores were being shot out of the cups one by one with consid¬ 
erable force like popped com jumping out of the popper. When recently 
matured aecidia were dissected out of the leaf and placed on slides in 
damp chambers overnight, it was found that a fan-shaped spore print 
1 Received for publication Feb. n, 1924. 
2 Reference is made by number (italic) to “Literature cited,” p. 756 
Journal of Agricultural Research, 
Washington, D. C. 
(749) 
Vol. XXVII, No. 10 
March 8, 1924 
Key No. G-377 
