8 BULLETIN 629, U. S. DEPARTMENT OF AGRICULTURE. 
Morgenthaler (9) conducted experiments to determine the effect 
of various influencing factors on the production of teliospores and 
found that " the time of appearance of the teleutospore stage is not 
dependent alone on the season of the year, but may be hastened or 
retarded by many other influences." He also states — 
It is also true that the chemical constitution of the host may provide condi- 
tions either favorable or unfavorable for the nourishment of a particular para- 
site. There are cases known in which the same rust will produce uredospores 
copiously on one host and only sparingly on another. There may be in certain 
host plants substances toxic to the fungus, as tannin, which further influence 
the nourishment of the parasite, and with it its spore production. 
This ability of various conditions to influence teleutospore production may 
also be regarded as a method of protection which the rusts have against 
influences which are unfavorable for the normal development of the fungus. 
EXPERIMENTAL DATA. 
Table I presents the results of all the varietal tests, including inocu- 
lations of both rusts made on seedling plants and on the plants at 
time of heading. The inoculations made were as follows : 
Stem rust: 
Seedlings 1.256 
Headed plants 260 
Crown rust : 
Seedlings 1. 480 
Headed plants 260 
Total 3,256 
The varieties are arranged alphabetically by name in Table I, 
except that those bearing the Latin names under which they were 
received are placed in a separate list, as are also the varieties of red 
oats which are derivatives of Avena sterilis. 
The greenhouse number (column 2), the classification list number 
(column 3), the Cereal Investigations number (column 4), the Seed 
and Plant Introduction number (column 5), and the Minnesota Ag- 
ricultural Experiment Station number (column 6) are included in 
Table I in order that identification may be more certain. It is thus 
quite possible to compare the record of any variety in this list with 
statements made in literature regarding it or with field records. 
In columns 7 to 10 of Table I the letter S indicates the undoubted 
and complete susceptibility of that variety under the conditions of 
the experiment. A question mark (?), S?. or E? indicates some 
doubt and the need of further tests, while E -f- S indicates that both 
resistant and susceptible plants were observed. The letter E has been 
used only where normal infection did not occur. In these instances 
the evidence seemed convincing that plants of the variety when tested 
in the manner here described prevented the formation of normal 
uredinia and may therefore be regarded as resistant. In a great 
