982 
Journal of Agricultural Research 
Vol.XXIV,No la 
The material was a part of that which was being used for the purpose of 
obtaining resistant wheat for growing in the Northwest. This problem 
was being cooperatively investigated by the Sections of Plant Breeding 
and Plant Padiology of the Minnesota Agricultural Experiment Station, 
and the Office of Cereal Investigations of the United States Department 
of Agriculture. The individually harvested Fg plants were furnished to 
the present writers. The biologic forms of rust were some of those 
which were being studied by M. N. Levine. 
Plants of each Fg family were grown in 4-inch pots in the greenhouse, 
one family in each pot. All pots of soil were steam sterilized imme¬ 
diately before use and the seed w^as sovm at a uniform depth. A large 
proportion of the hybrid seed as well as of the parental seed was infected 
with Helminthosporiura and consequently the number of plants per pot 
varied between 8 and 20. The seedlings were grown in a seedling 
section of the greenhouse in which no rust-infected plants were kept. 
When they were about 3 inches high they were inoculated with fresh 
urediniospores of one of the two forms used. Only one rust form was 
worked with at one time. The pots were then placed in an incubation 
chamber for 40 to 48 hours with a number of control pots of the parental 
varieties inoculated in the same way. The two forms of rust were kept 
on well-separated benches to avoid accidental contamination of one 
with the other. An attempt was made to keep the temperature, mois¬ 
ture, and light condition the same for all plants. The methods used 
were essentially the same as those described by Stakman and Piemeisel 
Notes on the character of infection with both forms were taken from 
15 to 19 days after the date of inoculation. The amount and rapidity 
of rust development was found to vary in response to environmental 
conditions. However, the character of infection was found fairly 
constant within certain limits, regardless of external influences. 
The Fg seedling plants were inoculated in sets of about 25 to 40 pots 
each. The total interval during which results were being recorded for 
the reaction to any one biologic form was approximately two weeks. 
In addition to running control plants of the parental varieties with ^ach 
set of hybrid plants, one or more complete sets of “differentiar* varieties 
were inoculated during work with each form. In this way a complete 
control was obtained on the identity of the form being used. The 
differential varieties used were as follows: Little Club (C. I. 4066); 
Marquis; Kanred; Kota (C. I. 5878); Arnautka (C. I. 4072); Kubanka 
(C. I. 2094); Mindum (Minn. No. 470); Acme; Binkom (C. I. 2433); 
Vernal emmer (Minn. No. 1165); and I^apli emmer (C. I. 4013). 
The percentage of infected plants obtained, on the average, was very 
satisfactory. Of a total of more than 10,321 plants which were inoculated 
796 showed no infection. 
In recording the types of infection the symbols prepared by Stakman' 
and Levine (25a) in their work on biologic specialization were used'. 
These classes of host reaction and of corresponding types of infection 
resulting from inoculation of seedling wheat plants with spores of 
Puccinia graminis tritici are as follows: 
