184 Transactions British Mycological Society. 



developing apothecia. In the spring these ridges rupture along 

 their crests by longitudinal fissures which expose the white 

 hymenium beneath. 



Internal Appearance. 

 For the purpose of studjdng the development of the parasite 

 in relation to its host, fixations of material were made each 

 week. The preparations were cut with a microtome at a thickness 

 of 5/x and stained with various modifications of Flemming's 

 Triple Stain. 



1. Infection. Infection as noted by Miiller is produced by 

 means of the ascospore. This adheres to the under surface of 

 the leaf by means of its gelatinous sheath and if near a stoma 

 sends out a germ tube which grows through a stomatal pore. 

 The fungus branches sparingly in the air spaces, lower epidermis 

 and spongy mesophyll of the leaf. It is, however, intra-cellular 

 and ramifies throughout the cells of the pahsade tissue, becoming 

 especially concentrated in the cells of the upper epidermis. 

 Here, further growth of the hyphae, chiefly in the vertical 

 direction, causes a pressure upon the inner and outer walls of 

 the epidermal cells and a consequent rupture of the vertical 

 walls (fig. i) . This does not agree with the observations made by 

 Miiller, who states that the hyphae are not in the cells of the 

 upper epidermis but that the fungus develops between the 

 cuticle and the cell walls. Further, it is possible to see, in this 

 and subsequent stages of the fungus, the cuticle still in contact 

 with the outer epidermal walls. This stage in the Hfe-history 

 may be regarded as the end of the incubation period and corre- 

 sponds with the appearance of the yellow spots on the leaves. 



2. Sclerotium. In sections cut when the dotted black sclerotia 

 are visible on the leaves, the outer cell walls of the upper 

 epidermal cells exhibit a conspicuous blackening. The cells them- 

 selves are rich in a fatty brownish material which, it would 

 appear, is secreted by the hyphae and laid down upon the cell 

 wall which gradually changes from brown to black (fig. 2). The 

 sclerotium remains in this condition during the summer or 

 conidial stage of the fungus. During the formation of the 

 apothecia the sclerotium becomes greatly thickened by the 

 activities of the hyphae which form a hard, black, plectenchyma 

 beneath the originally thickened cell walls (fig. 4). Sclerotium 

 formation also occurs to a much lesser extent in the cells of the 

 lower epidermis (fig. 4). ,,-.,• 



3. Pycnidia. The hyphae below the early formed sclerotmm 

 become arranged in a vertical series (fig. 2), giving rise to a 

 number of unbranched conidiophores. The contents of these 

 hyphae stain most deeply at the apices and rod-shaped conidia 



