Arthur S. Horne and Eleanor Violet Horne 199 



yielded Polyopeus purpureus, but with Fusarium mail in addition. 

 Another natural spot yielded an unidentified fungus. In this variety, 

 Pleospora has made no progress, but a different fungus, Polyopeus 

 purpureus, occurring in the natural spots on the same apple, has effected 

 an entry 1 at the points where Pleospora was introduced. Again Pleospora 

 was not re-isolated from Lane's Prince Albert, a variety with a wider sea- 

 sonal range (Oct.-Mar.), but Polyopeus purpureus and another phomoid 

 fungus were obtained instead from the artificially produced spots. 



The results obtained in Grenadier (Sept.-Oct.) were somewhat 

 different. Small brown spots appeared at the point of inoculation on 

 Sept. 12th. These measured 3 mm. in diameter on Sept. 24th. On this 

 date other spots were forming at the lenticels near the point of inocula- 

 tion. A month later the original spots formed merely the nucleus of 

 brown areas ; in fact the apple was in a semi-rotten condition. On Nov. 8th 

 fragments of tissue removed with sterile instruments from the diseased 

 area near the original point of inoculation were placed on the surface 

 of apple agar in slant tubes. After a few days Polyopeus purpureus and 

 Alternaria grossularieae were present in the cultures. Cultures made in 

 the same way but using tissue taken 2 ins. from the point of inocula- 

 tion yielded Alternaria grossularieae. Finally, cultures made using 

 eruptive mycelium taken from pustules appearing at the surface of 

 the apple (Oct. 29th) yielded Polyopeus purpureus. Pleospora pomorum 

 was not obtained at all, but instead two other fungi — Polyopeus purpureus 

 and Alternaria grossularieae — which were not present in the inoculant. 



6. Control. 



Susceptibility and Immunity. 



This work has shown (Section 5) that Pleospora pomorum can para- 

 sitise at least three varieties of apple (Rival, Wealthy, Allington Pippin), 

 whilst in certain other varieties (Cardinal, Grenadier, Potts's Seedling), 

 originally inoculated with Pleospora, Pleospora was either not re-isolated 

 (Polyopeus purpureus was obtained instead) or was re-isolated in associa- 

 tion with other fungi (Polyopeus purpureus, Alternaria grossularieae, etc.). 

 Considering together the observations noted in Section 4 and the facts 

 recorded in Section 5, the evidence seems to suggest that both Pleospora 

 pomorum and Polyopeus purpureus exhibit a preference for varieties, 



1 It is interesting to note in Norfolk Bcaufin (Oct. -Dec.) artificially made punctures 

 were not inoculated by the fungus or fungi causing the natural spots formed in October 

 on the inoculated specimen. 



