May 31,1924 Expulsion of Aecidiospores by the Mayapple Rust 
925 
be shot horizontally when projected from the aecidium. In other words, if the 
same force is applied to shoot a toy balloon upward vertically as is applied to 
throw it horizontally, the distance traversed by the balloon before it begins to 
fall in a straight line is about the same in both cases. 
As only a few spores in each experiment were found at a distance of cm. 
from the aecidia, this may be assumed to be about the maximum horizontal 
distance that the spores could be thrown under these conditions. In the limited 
number of trials made to determine how high the spores could be shot the max¬ 
imum distance seems to have been about 1 cm. No doubt if the experiments 
had been made with the rust on leaves attached to the plant the results would 
have been somewhat different. 
SPORE DISCHARGE FROM AECIDIA OF GYMNOCONIA INTER- 
STITIALIS 
Similar experiments were performed with orange-rust aecidia on leaves of 
Rubus. When small pieces of leaves bearing aecidia were employed the spores 
were shot vertically about 1 cm. but when entire leaves were used the vertical 
distance covered was somewhat greater, 1.3 cm. in some cases. Entire leaves 
were not used to determine the maximum horizontal distance. Using small 
squares of infected leaves, it was found that the maximum distance was about 
1.1 cm. It makes a great deal of difference which orange-rust of Rubus is 
used in these experiments. The spores of the short-cycled form are rather 
waxy and tend to cling together so that they pile up in the sorus. Occasionally 
some of the spores are set free singly with a small amount of force so that they 
are found a few millimeters from their aecidia. On the other hand, when the 
long-cycled orange-rust is used a dusty spore print is laid down. 
PORE FORMATION IN AECIDIOSPORES OF PUCCINIA PODOPHYLLI 
The first thing that particularly attracts attention in the examination of a 
spore print of the Podophyllum rust under the microscope is the large number 
of little bodies which lie around on the agar among the spores and attached 
to them. (PI. 1.) These bodies resemble closely the “pore plugs” found at¬ 
tached to the spores of the bayberry rust previously mentioned. In order to 
prove whether or not they had the same origin, it was found necessary to study 
sections of young aecidia. Small pieces of leaf which showed the first signs 
of aecidial growth were fixed in Flemming’s weaker fluid. Sections were stained 
with the triple stain. 5 In case of the Myrica rust the first indications of pore 
formation is seen in connection with the fourth or fifth spore in the chain. The 
process certainly begins earlier with the Podophyllum rust, for .the second spore 
in the chain frequently shows one or two places where the wall is being dis¬ 
organized around a thickened portion which takes the gentian violet stain. 
(Fig. 1, A.) The older the spore the larger the plugs become. If there are 
six or seven spores in the chain the plugs in the upper ones are so large as to 
indent deeply the walls of adjacent spores. In stained preparations the plug 
appears to lie in a cavity somewhat larger than the plug. There is no doubt 
that there is a certain amount of mucilaginous disorganization accompanying 
pore formation which also adds to the pressure, tending to spring back, or in¬ 
dent, the spore walls. The peridial cells at the upper end of a chain of spores 
never show germ pores or pore plugs. (Fig. 1, A.) 
In favorably oriented sections three or four germ pores can be seen in one 
spore. (Fig. 1, D.) Exceptionally large pore plugs are shown in figure 1, C. 
6 Miss Ruth Colvin prepared the slides for this study and made the photographs which are reproduced 
in this paper. 
