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 R? indicates some 

 doubt and the need of further tests, while R + S indicates that both 

 resistant and susceptible plants were observed. The letter R 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 



