July is, 1914 
Influence of Host on Puccinia 
3i3 
Viola used in each set of inoculations. In many instances the infection 
of the species of Pentstemon was very abundant and vigorous. This 
was especially true when the leaves of the Pentstemon sp. were at their 
optimum period of susceptibility. 
Puccinia ellisiana did not infect the species of Pentstemon as abun¬ 
dantly as it did certain highly susceptible species of Viola. Nevertheless 
the infection of Pentstemon sp. was so great in many cases that if the 
material had been contaminated with Puccinia andropogonis the thin- 
walled, echinulate urediniospores characteristic of this rust would easily 
have been found in the culture material. In not a single instance was 
there a failure to infect the Pentstemon plants with Puccinia ellisiana if 
the leaves had reached their susceptible period. Two to four pots of 
species of Pentstemon were used in every set of inoculations, and not only 
was every plant infected, but in many instances every leaf and even the 
stem was attacked. In some cases the leaves were so badly infected that 
they died before all of the aecia opened. 
When either lt Puccinia ellisiana from Pentstemon” or the ordinary 
Puccinia andropogonis was used, the inoculated species of Pentstemon 
were more vigorously and abundantly infected than when typical Puccinia 
ellisiana material was used. However, when the attempt to carry 
“Puccinia ellisiana from Pentstemon” back to Viola was made, the rust 
would and did go on to Viola, but with great difficulty. 
The data given in the tables do not show this condition fully, for out 
of nearly 50 pots of Viola spp. inoculated only 8 plants were infected. 
On these 8 plants the infection was very meager. On each of 2 of 
these plants three leaves were infected, but on each of the other 6 
only one leaf was infected and only one sorus to a leaf developed. This 
is also true of Puccinia andropogonis . It will infect certain species of 
Viola, as the culture table shows, but only very sparingly and then only 
under the most favorable conditions. 
The teliosporic culture material of “ Puccinia ellisiana from Pentste¬ 
mon” must be very virile and used in large quantities under the most 
favorable culture conditions and on a large number of plants of Viola 
to obtain any infection whatever; and when infection does occur only an 
occasional leaf out of a large number develops a sorus, while the check 
plants of Pentstemon used with Viola spp. under the same bell jar or in 
the same inoculating chamber are literally covered with sori. This 
means that hundreds of viable sporidia were discharged on to the violets 
and that only an occasional one was able to establish a foothold in the 
tissues of the violet and finally produce aecia. With less virile teliosporic 
material and under less favorable culture conditions, inoculations made 
on species of Viola with either Puccinia andropogonis or with “Puccinia 
ellisiana from Pentstemon” would probably fail to infect a single plant. 
This is exactly what happened in the culture experiments of 1913. No 
