106 



"blisters are formed and the tissue is soon killed at the points of 

 infection. This often results in the formation of cracks, which con- 

 tinue to increase in size as the apple grows. The general appearance 

 in this case resembles that of apple scab. When the fruit is partly 

 ripe, large, brown, depressed patches are formed, the skin becomes 

 black and parchment-like, and numerous masses of Coniotheckim are 

 produced in the tissue. At a later stage, the Phoma form of fruit 

 bursts through the blackened skin. In the case of the fruit, infec- 

 tion takes place through the numerous minute ruptures of the skin 

 which are perhaps imperfectly-formed lenticels. 



Coniothedum has for some time been considered of doubtful generic 

 value.^ In "British Fungus Flora"* the following rider to the 

 generic diagnosis occurs : " Conidia usually very variable., resembling 

 conglomeration*? of cells of variable size. A very badly-defined genus, 

 and it is doubtful whether many of the so-called species are such in 

 reality." Mr. C. 0. Farquharson was the first to demonstrate that 

 Coniothedum resulted from the germination of Phoma spores, when 

 working at a water-lily disease in the -Jodrell laboratory, but the 

 investigation was not completed owing to his departure for Southern 

 Algeria as mycologist. He also proved that the spores of Phoma 

 abiehs, Br., produced a Coniothedum stage on germination, hence, in 

 luture, Coniothedum will only be retained as a form-genus until its 

 components are correlated with their respective Phoma forms. • 



The Phoma stage appears in great abundance in the spring on 

 shoots and spurs killed by the Coniothedum the previous year. From 

 other species of Phoma occurring on the same hosts, P. mali is readily 

 distinguished by the form of the perithecium and the spores. The 

 penthecium IS very much vertically depressed, so that a section is 

 irregularly biconvex. The spores are fusiform or spindle-shaped and 

 measure 7-8 x 2-3 m- Spores of the Phoma placed on sterilised 

 apple shoots were found to enter the tissue only through the lenticels. 

 On germination a weft of very delicate hyaline mycelium sur- 



iV fi • 1 1 ; -"^^"l^v:>.^, wuBiB iney increasea consiaerauij' 



m tlnckness and gradually assumed an olive-green colour, and gave 

 ongm to typical Cwuoihedum groups of cells. In all probability the 

 niycelium first produced by the spores lives as a saprophyte, obtaining 

 Its tood from the dead tissue of the lenticel, and afterwards assumes 

 a parasitic habit. The parasitic phase i«, however, not absolutely 

 necessary, as when Phoma spores are sown in a nutrient medium the 

 U,uoihecmm and Phoma stages are produced in due course. This, 



rXT'"' f ""J ^""^ ^'''^''^ ^^ "^t^^^^' as f ^ave not succeeded in 

 infecting dead shoots with either Coniothedum or Phoma spores. 



won d ,^f 'serous form of fruit is rare, and, as in many other cases, 



he lX^''''-.V P ^^ ^"^ "" unimportant part in the continuation of 



ekh^rT.' \fT ''.r^'^' ^^"^'-^ ""' «Pa^«- It occurs on dead twigs 



w th H?i ^•'' ' ^''' ^^'"^'' ""' ^^ ^ ^^ter stage. I have only met 



he ir' Th'^' '^^^ ^''''~°" ^^^^^ apple twigs, accompanying 

 me Ihoma. Ihe ascig^rous snav^« ««„,« 'J ..„?_ '^ „--j.-f,-„^...^- 



ine ascig^rous spores sown on a nutrient medium pro 



^homa 



gave orimii to the 



^.^.^ ^"rt 



um : the latter, how - 



# 



Alassee, G., Brit. Fundus Flora, 3, p. .127 (189;J). 



