CONTRIBUTIONS FROM THE WLSLEY LABORATORY. 



507 



frequently the cause of what is called the ' black ' disease of wheat. 

 In the last case Lopriore * has proved its capability of infecting living 

 wheat plants; while Janczewskif has shown that the attack depends 

 largely upon climatic conditions. 



In infection experiments carried out at Wisley during the past season, 

 by applying living spores of the fungus to the surface of the leaf of the 

 apple and protecting the infected leaves from outside infection, it was 

 proved that the fungus was capable of attacking healthy leaves of at 

 least some varieties (the majority of those experimented with) and pro- 

 ducing upon them the typical spots as described above, and later (in the 

 course of about five or six weeks) the fruiting form of the fungus. 

 Infection probably takes place mainly through the stomata, since the 

 germ tubes of the fungus have been seen making their way into the 

 leaf by these openings. In one case, however, infection occurred when 

 the spores were applied only to the upper surface of the leaf, but a slight 



B 



Fig. 91. — Cladosporium herbarcm in Apple Leaf. 



a, Cells of leaf (upper surface) ; b, mycelium of fungus ; c, microsclerotium ; 

 d, conidiophores ; e, f, spores, a-e, much magnified ; p, more highly 

 magnified. 



injury to the epidermis of the leaf in this case may have given the 

 opportunity for the fungus to gain an entrance. The dark mycelium of 

 the fungus grows through the tissues of the leaf causing the death of 

 the cells, and after a time forms several compact masses of almost 

 spherical shape, measuring about '12mm. in diameter. These bodies, 

 which are known as microsclerotia, are of a black colour, and are formed 

 just below the epidermis of the leaf (fig. 91, a, b, c). They may be seen 



Men des points de l'ouest et du centre de la France, et l'an dernier encore, ont perdu 

 de bonne heure une grande partie de leur feuilles qui se dessechaient sur leur bords 

 et tombaient. Les fruits mal nourris etaient arretes dans leur developpement et ne 

 donnaient qu'une recolte des plus mediocres. Nous avons recolte, rec,;u et examine 

 de nombreux echantillons de ces feuilles malades, a demi-dessechees, provenant 

 surtout de la Normandie, du Maine, du Perche et de la Bretagne, toujours sur les 

 places dessechees nous avons trouve en abondance des touffes de Cladosporium 

 [herbaruni]. . . . Nous poursuivons des essais de culture de ces Cladospoi ium, sur 

 le controle de l'experience est necessaire pour 6tablir d'une fa^on certaine si le 

 Cladosporium, ou une des formes s'y rapportant, envahit, comme nous le pensons, 

 les feuilles vivantes du pommier . . . et est la cause des alterations que nous venons 

 de signaler." 



* " Die Schwarze des Getreides," Landwirtsch. Jahr. xxiii. 1894, &c. 

 f " Recherches sur le Cladosporium herbarum et ses compagnons habituels sur 

 les cereales " in Bull, de V Acad, des Set. de Cracovie, 1894. 



