494 
Journal of Agricultural Research 
Vol. XXV. No. xa 
spread the Gymnoconia, with its somewhat dry and dusty spores, from 
western Europe through Russia into Siberia and across the straits to 
Alaska. From there it probably followed the coast and crossed the 
continent from west to east and from north to south. Many addi¬ 
tional susceptible species of host were met in America, at the same time 
that widely different climatic conditions were encountered, all of which 
favored a change of life habits by the rust, which culminated in the elimi¬ 
nation of the teleutosporic stage entirely. Until some one has secured 
systemic infection of blackberry directly by sowing aecidiospores from 
the raspberry, which Kunkel says sometimes produce promycelia, 
and has obtained a systemic rust at once comparable to our common 
short-cycled rust, the writer sees no valid reason why separate specific 
or even generic names might not be applied to two forms which are well 
fixed. The third or intermediate type which is maturing aecidia of 
two kinds may represent a strain of Gymnoconia which is particularly 
unstable and from which a short-cycled rust is now arising and which will 
have distinct morphological characters of its own. 
As the writer understands Kunkel’s 6 conception of the two life cycles 
involved in the Gymnoconia, the aecidiospores are all alike in that, 
especially if germination can be delayed by lowering the temperature, 
a few normal as well as abnormal promycelia are apt to be found in 
almost any germination test. This may very well be the true nature of 
the common Gymnoconia, but the form of the rust which produces two 
kinds of aecidia is in an entirely different category. In this form the 
nature of the aecidiospore, whether it is to produce a germ tube or a 
promycelium, is predetermined as it is being matured. The fusion in 
the spore of its two nuclei might very well be accompanied by changes in 
the coloration of the spore contents and in the nature of the spore wall, 
but by no kind of treatment during germination could a normal aecidio¬ 
spore germ tube be obtained. On the other hand, precocious nuclear 
fusion, either in the spore or in its tube, might be induced by some 
external treatment so that a promycelium with sporidia would follow. 
In case such sporidia were capable of infecting the host, we should 
expect the rust to go back to its former habits in the new generation 
resulting from this infection. The nature of the germ plasm is believed 
not to be easily and permanently altered by environmental changes. 
The writer has given reasons for believing that the production here of 
two kinds of aecidia on the same leaf is due to the variable nature 
of a strain of the Gymnoconia which normally includes the old Puccinia 
peckiana in its life cycle. 
Whatever may be one's view regarding the manner of the origin of a 
species, and whether in this case we say a species is arising as the result 
of hybridization or by mutation, it is clear that the practice of applying 
the terms telium and teliospore to the aecidium and aecidiospore of a 
short-cycled rust just because the aecidiospore happens to produce a 
promycelium instead of a germ tube can no longer be defended. Such 
terms should represent morphological units, and not behavior. No 
doubt a study of the individual aecidia of a number of other rusts which 
were shown by Jackson at the Boston meeting of the Botanical Society 
of America to have correlated short and long cycled forms will bring 
forward additional evidence to prove that what we are pleased to call 
species are arising to-day as they have arisen for ages past. 
8 Kunkel, I,. O. further data on the orange-rusts of rubus. In Jour. Agr. Research, v.19, 
p. 50X-512, pi. D, 93-94. 1920. Literature cited, p. 5x2. 
