754 
Journal of Agricultural Research voi. xxvn, No. io 
are also being discharged with considerable violence. If a Petri dish 
containing a thin layer of agar is inverted and a leaf bearing aecidia is 
placed in the cover so that the surface of the leaf which is covered with 
aecidia faces upward, it can be proved that the spores are frequently 
thrown vertically to a distance of 4 or 5 mm. or more. Many spores 
not hitting the agar, or if so, not sticking, fall back on the leaf or 
on the glass at some distance. Further study of the mechanics of 
spore discharge by the orange-rust will certainly prove interesting. 
These spores are not very waxy and tend to fall out of the sori soon after 
maturity, and they can stand a certain amount of drying. There is, 
however, enough wax on the exospore to insure that many of the spores 
as they fall will stick to the other leaves of the plant on which they 
were originally developed. By this compromise we find that teleutospores 
are commonly developed on the original host plant as well as on plants 
some distance away. The waxy coating is more highly developed on 
the aecidiospores of the short-cycled orange-rust, and as noted previously, 
this tends to hold the spores together in the sorus on the leaves well 
above the ground. Germinating in this position the resulting sporidia, 
well adapted for dispersal by air currents, begin their flight from an 
elevated position. The teleutospores of Puccinia malvacearum germi¬ 
nate in the sori as they hang on the living leaves, as soon as they are 
mature. 
If one desires to infect a root shoot of a blackberry with the short- 
cycled orange-rust, he will be more successful if he sows sporidia on the 
shoot. If he sows aecidiospores he will be less successful; one reason for 
this may be that the sporidia which are to produce the infection are dis¬ 
charged from the promycelia with sufficient force to carry them away 
from the very place where they should come to rest if infection is to be 
obtained. 
Not all of the aecidia of the bayberry rust are borne on the under side 
of the leaves. In many cases the ends of young branches and the fruit 
buds are covered with them so that the cups open out in all directions. 
This is especially true of the rust on the “sweet fern/’ Comptonia, 
where the burlike fruits and entire terminal parts of certain branches 
are attacked. The leaves bearing aecidia are also contorted and coiled 
into a form resembling that of a ram's horn (4). Such locations bring 
the aecidia into positions unfavorable for spore discharge unless the spores 
are started off with an initial impulse. Without entering into an exten¬ 
sive discussion of the formation of germ pores in other types of spores, 
it may be interesting to note that Strasburger and others have studied 
pore formation in the walls of pollen grains of several species of plants, 
and further that there are homologies and analogies between the 1 pore 
plugs described above and germ pore lids in certain pollen grains. 
Strasburger ( 8 ) in his well-known Work on the structure and growth of 
cell membranes describes the development of the walls and germ pores 
of several different kinds of pollen. Two layers are differentiated; the 
outer layer is referred to as the exinium, or exine, which is commonly 
called the exospore. An inner layer Strasburger identifies by the terms 
intinium or intine (endospore). In the geranium ( 8 ) (fig. 27-38), thick¬ 
ening of the outer wall of the pollen grain does not occur at certain 
points. These thin places in the wall are the germ pores. Due to 
pressure from within, some of the cytoplasmic contents of the cell along 
with some of the endospore, are forced through the germ pores and form 
papillae. The granular contents become lined up in striae and stain 
