88 MendeUan Inheritance and Yelloir Rust in Whnil 



also flecked, and the former had 8 pustules, some ol wliich shed 

 spores. 



On bed B (row 2), 1 jilaiit was slightly flecked, and another bore a 

 few unbroken pustules on one blade. In row 10 the 4 plants remained 

 free from infection. In row 6 there were only 2 plants; one of these had 

 14 leaves badly attacked and on these over 200 pustules were counted, 

 many of which were freely shedding spores. Some weeks later it was 

 discovered that this plant was also infected wnth Bunt (Tilhtia cariefsy. 



Turning next to the extracted resistant types it is seen that the 

 plants of (}&j9/d (row 4) on beds C and D were completely resistant on 

 June 2nd; further, they remained immune to the end of the season. 

 On bed A, 4 plants out of 19 had sHght attacks, in each case a few 

 pustules were formed, some of which were broken. On B, 2 out of the 

 3 plants had a few slight "flecks," but no pustules were seen. On the 

 whole therefore this extracted f\ type was distinctly more resistant than 

 its resistant parent (American Club) under these abnormal conditions. 



All the plants of the extracted resistant type 82/14/'/ (row 8) re- 

 mained free from any trace of infection throughout on beds A, C and D. 

 The 2 plants on bed B each had a shght attack on one blade. On one of 

 these the attack was confined to the leaf-tip where the tissue was dying 

 off. This extracted type was then decidedly more stable in its resistance 

 than American Club. 



In summing up, it may be repeated that the conditions under w^hich 

 these plants were grown were much more unfavourable to rust resistance 

 than those Ukely to be met with in general farm practice. This is especi- 

 ally true of beds A and B. During the latter part of May and throughout 

 June the susceptible varieties produced enormous quantities of uredo- 

 spores and the alternating rows of resistant cultures were literally 

 powdered all over day by day with fresh spores. It is conceivable that 

 an occasional spore may possess more than the average power for bringing 

 about an infection, and with such iiuge numbers of inoculations occurring 

 day by day it is not surprising that now and then infection should have 

 been accomphshed. 



But the evidence shows that the success of the parasite was of a 

 very limited nature. Later observations indicated that the position on 

 June 2nd was the worst reached during the year. Not only did the fungus 



' Since then another similar case has been observed. In an F, culture (from the cross 

 Wilhelmina x American Clul)) raised from an immune F^ plant all except one plant were 

 rust-free. This odd plant wa.s very severely attacked by rust, ajid was also found to be in- 



fecteit with Hunt. 



