EXPULSION OF AECIDIOSPORES BY THE MAYAPPLE 
RUST, PUCCINIA PODOPHYLLI SCHW 1 
By B. O. Dodge 
Pathologist , Office of Fruit-Disease Investigations , Bureau of Plant Industry , 
United States Department of Agriculture 
The mechanics of spore discharge from an aecidium was recently discussed in 
a short account of the formation of germ pores of aecidiospores of Gymnosporan - 
gium myricatum . 2 The aecidiospore of the bayberry rust is provided with germ 
pores, six or seven in most cases. The writer found that, at the point where a 
germ pore is to be developed, there is a thickening of the spore wall over a small 
area in such a way that there is formed a little ball-like body, or “pore plug,” 
which is separated from the rest of the spore wall. The germ pore becomes evi¬ 
dent as soon as the plug is dislodged. By studying carefully stained sections of 
young aecidia it may be seen that the plug or pore formation begins with about 
the fourth spore in the chain and is completed when the spore reaches maturity. 
Seeing the spores densely packed in an aecidium, and with the spore walls deeply 
indented by the plugs, one readily understands how the plugs function in pro¬ 
viding a more effective mechanism of spore discharge. Although the aecidiospore 
of the long-cycled orange-rust, Gymnoconia, on Rubus, does not form such pore 
plugs, still the spore is discharged with considerable force, proving that the plug, 
though serving a useful purpose in this connection, must act only in an accessory 
capacity in dislodging the spores in case of the bayberry rust. In view of the 
fact that such bodies have not been reported by those investigators who have 
studied the cytology of the rusts, it was thought likely that the persistence of 
that part of the spore wall as a little plug or ball filling or covering the germ pore 
was rather an unusual occurence. The writer has found a second species of rust 
where pore formation is accompanied by the development of similar bodies which 
persist as little plugs and no doubt take part in forcibly discharging the spores 
from the aecidium. 
THE MAYAPPLE RUST, PUCCINIA PODOPHYLLI 
The aecidia of Puccinia podophylli frequently cover large areas of the leaf so 
that the normal functioning of the lower epidermis must be seriously interfered 
with. The orange-rusts of Rubus are perennial. It was pointed out by the 
writer 3 that the presence of the gametophytic mycelium so stimulates the host 
that large numbers of stomata are formed on the upper side of the leaf where 
normally there are none. A similar study of Podophyllum leaves heavily 
infected with the mayapple rust sufficed to show that no such an effect 
follows the invasion of a leaf in this case. Stomata were rarely found on the 
upper side of the leaf, whether infected or not. Although the results of this 
study were disappointing, some further information was obtained relative to the 
discharge of the secidiospores. 
1 Received for publication July 23, 1924—issued Nov., 1924. 
2 Dodge, B. O. aecidiospore discharge as related to the character of the spore wall. Jour. 
Agr. Research 27: 749-765, illus. 1924. 
* Dodge, B. O.— Effect of the orange-rusts of rubus on the development and distribution of 
stomata. Jour. Agr. Research 25: 495-500, illus. 1923. 
Journal of Agricultural Research, 
Washington, D. C. 
( 923 ) 
Vol. XXVIII, No. 9 
May 31, 1924 
Key No. G-368 
