316 
Journal of Agricultural Research 
Vol. II, No. 4 
MORPHOLOGICAL CHARACTERS 
When Puccinia ellisiana infects Pentstemon and the resulting gecio- 
spores are sown on Andropogon, the urediniospores thus obtained are 
no longer typical Puccinia ellisiana spores, but have the thin echinulate 
walls characteristic of the ordinary Pentstemon rust, Puccinia andro- 
pogonis. When the teliosporic material thus obtained is sown on species 
of Viola and the aeciospores from the infected violets are sown on Andro¬ 
pogon, the resulting urediniospores go back to the form typical of the 
regular Viola rust, Puccinia ellisiana . In other words, if the regular 
rust of Viola passes through Pentstemon, it develops urediniospores of 
the ordinary Pentstemon rust, Puccinia andropogonis; if it is now passed 
back through Viola spp., it develops the urediniospores of the typical 
Viola rust, Puccinia ellisiana. If, on the other hand, Puccinia andro¬ 
pogonis is sown on both Viola and Pentstemon, the Viola spp. will be 
very sparingly infected, as previously stated, and the aeciospores from 
this infection when sown on Andropogon produce urediniospores typical 
of the regular Viola rust, Puccinia ellisiana , while if the same teliosporic 
material is sown on Pentstemon and the aeciospores thus obtained are 
sown on Andropogon, urediniospores typical of the Pentstemon rust are 
developed. In each case the determining factor as to the characters of 
the urediniospores is the aecial host. This fact can be more clearly 
shown by the following diagram: 
Diagram Showing Plan of Cross-Inoculations with Puccinia Ellisiana and 
P. Andropogonis 
(i) 
1913 - 
Viola to Andropogon 
(P. ellisiana). 
1912. 
Andropogon 1 
(.Puccinia ellisiana) .< 
I 9 I 3- 
Pentstemon to Andropogon 
(P. andro¬ 
pogonis). 
1914. 
Viola to Andropogon 
(P, ellisiana). 
1914. 
Pentstemon to Andropogon 
(P. andropo¬ 
gonis). 
1914. 
Viola to Andropogon 
(P. ellisiana). 
I 9 I 4- 
Pentstemon to Andropogon 
(P. andropo¬ 
gonis). 
I 9 1 3- 
Andropogon 
(Puccinia andropogonis). 
1914. 
Viola to Andropogon 
(P. ellisiana). 
1914. 
Pentstemon to Andropogon 
(P. andropogonis ). 
All of the experiments represented in the above diagram were per¬ 
formed and all of the culture material used, both telial and aecial, was 
grown under control conditions in the Bureau of Plant Industry green¬ 
houses at Washington, D. C. This diagram represents not only what 
