Nov., 1921] HOERNER — ^ STUDIES ON THE CROWN RUST OF OATS 
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inoculation a profuse production of teliospores was noted on every plant in 
one of the pots that had been kept in the dark. (See figure i, Plate XXIV.) 
V 
The appearance of a purple pigment surrounding infected areas of the 
oat leaves inoculated with crown rust is not uncommon. The variety of the 
host plant, its age before inoculation, the length of time of infection, the 
history of the inoculum, its method of application, and all other externally 
visible environmental factors seem to have no direct correlation with this 
phenomenon of pigment formiation. 
Wheldale (7), regarding this anthocyanin pigment formation in plants 
attacked by fungi, says: 
It is frequently found that the pathological conditions called forth by the attacks of 
fungi are acconipanied by abnormal development of anthocyanin. In leaves of Tussilago, 
for instance, infected by Puccinia, a circular band of anthocyanin often appears surrounding 
the aecidium spots. . . . Injury to the living tissues of the conducting system of the veins, 
midrib or petiole of the leaf, or of corresponding tissues in the stem, leads to an accumulation 
of synthetic products in the leaves. ... It seems likely also that parasitic growths may 
interfere with the progress of the translocation current through the small veins of the leaf, 
thereby causing congested areas to arise in which the sugar contents are above normal. 
But it is conceivable that the pathological condition resultant on fungal attacks may be 
the direct cause, in some way, of pigment formation. 
In view of this interpretation and of the relatively general occurrence of 
this anthocyanin pigmentation during the course of the studies recorded in 
this paper, the assumption seems justified that pigment formation, as a 
phenomenon connected with the infection of oats by P. coronata Cda., is 
not a sign of resistance on the part of the host to the attacks of the rust 
parasite. 
VI 
Parker (8), speaking of early production of telia on oat seedlings, says: 
It is certain that in the hundreds of seedlings described as very susceptible in the 
present experiments telia were not produced on a single one following a normal and abundant 
production of uredinia. 
In the investigations reported in this paper, this was not the case. 
Although certain oat varieties showing resistance to attacks of the crown 
rust did produce telia, other very susceptible varieties also produced telia 
freely and in great abundance. Super-susceptibility on the part of the host 
may bring about the formation of telia due to conditions as explained by 
Wheldale, although resistant hosts may react in some way so as to be unfa- 
vorable to continued urediniospore production on the part of the fungus, and 
thus hasten the completion of its life cycle and the early production of telia. 
Parker has used this phenomenon of teliospore production, in certain 
cases, as a basis for the classification of resistant varieties. In view of 
results recorded here, such a basis for the classification of resistance would 
seem unreliable. Ligowa oats were listed as susceptible, and yet, during the 
