Mar. 8, 1924 
Aecidiospore Discharge in Relation to Spore Wall 
753 
strongly. Similarly, a tennis ball compressed over a marble on a table 
will be thrown farther upward when die confining pressure is suddenly 
removed than it will be if compressed against the table alone with the 
same force, and then released. 
Very little work has been done on aecidiospore discharge, so that it is 
impossible to explain the necesssity for any special device for insuring 
that the spores be ejected forcibly from the aecidium as soon as they 
mature. The aecidiospores of a great number of rusts are provided with 
germ pores and it is not unlikely that in some of the species the spores 
are thrown out with considerable velocity. It is conceivable that in 
some cases this would be of decided advantage to the rust. In the rust 
on Myrica most of the aecidia develop on the under side of the leaves (5). 
If the spores dropped out of the cup as soon as mature, they could be 
borne away by the wind just as well as if they had been shot out a short 
distance. On the other hand, these spores are rather short-lived and as 
they are somewhat waxy they would tend to cling or mass together in 
the cup and fall out in clumps as do the spores of the short-cycled orange- 
rust of Rubus (4). The aecidiospores of this blackberry rust develop 
sporidia on promycelia as they germinate, functioning as teleutospores. 
It is an unreported fact that these spores frequently germinate during 
wet weather or on warm dewy nights as they hang together in masses on 
the under side of the leaves. The spores are particularly fitted to function 
in this way by developing a waxy coating which holds them together. 
Sporidia developed on the under side of the leaves a few feet from the 
ground would be much more likely to be borne away by air currents 
than would the heavy aecidiospores themselves. 
The aecidiospores from roesteliae of other Gymnosporangia are cer¬ 
tainly not discharged with violence. The writer’s attention has not been 
attracted to any such persistent plugs developed in pore formation in 
roesteliae examined. In G. clavariaeforme where the germ pores are 
large and distinct from the first, the method of pore formation approaches 
that of pollen grains of geranium as described by Strasburger. In 
place of a thickened lid covering the pore, a granular substance is extruded 
which at first has the shape of a plug. It takes the orange G faintly and 
connects with the spore contents. The outer portion of the extruded 
mass is certainly not very different from the substance forming the 
thickenings on the exospore, but as the spore approaches maturity it is 
reabsorbed or withdrawn. The aecidiospores of this species, which are 
comparatively long-lived, collect in large quantities in the cancellate 
peridia and are allowed to escape through the hygroscopic action of the 
peridial cells. 
A beautiful example of modification of the coating of the exospore to 
better adapt the aecidiospore for proper distribution is found in connection 
with the orange-rusts on blackberry. There can be no question that the 
two orange-rusts are very closely related. The preponderance of evidence 
is that the short-cycled rust has been or is being derived from the long- 
cycled form. The aecidiospores of the latter should be distributed 
widely so as to bring about numbers of sporophytic infections in new 
regions. This large and irregular Gymnoconia aecidium is of the caeoma 
type and as the spores are not provided with germ pore plugs it is difficult 
to imagine how the spores can be so confined under pressure as to be dis¬ 
charged at maturity in any way comparable to the method worked out in 
the case of the bayberry rust. Nevertheless when we examine blackberry 
leaves bearing the long-cycled orange-rust, we find that these aecidiospores 
