2 Robinson, Puccinia iiialvaccannn mid its Jiost plant. 



maturity, germinate on the plant, and under normal con- 

 ditions produce pro-mycelia each bearing four sporidia. 

 The fungus is an autoecious member of the Uredinese, 

 which produces teleutospores only, and it has therefore 

 been classified in the sub-group Lepto-puccinia(Schroter). 



Little has been done on the intimate relations between 

 this fungus and the cells of the host. Attention has there- 

 fore been chiefly devoted to this, and to the histological 

 features of the diseased spot as compared with the corre- 

 sponding normal tissues. It will be convenient first to 

 describe the features of pustules on the petiole, stem and 

 leaf blade respectively, and then to describe the relations 

 between the individual cells of the host and the haustoria 

 of the fungus. 



The general relations of the fungus to the tissues of 

 the host plant are represented diagrammatically in Text- 

 figs 1-4. In the figures the distribution of the several 

 tissues of the host is mapped out and the area occupied 

 by the mycelium of the fungus is indicated by dots. The 

 mass of hyphae beneath the sorus is indicated by cross 

 hatching {c) and the sorus of teleutospores by vertical 

 lines (/). These figures, though diagrammatic, are in each 

 case founded on actual sections through characteristic 

 pustules. 



Text-fig. I represents a portion of a transverse section 

 through a petiole, with a pustule in a moderately advanced 

 stage of development. The petiolar structure is of an 

 ordinary dicotyledonous type. There is an epidermis 

 (^/.), a la}er of assimilating tissue {as), a band of coUen- 

 chyma {coll.), a cortical parenchyma of large cells {cor. 

 par.), and a ring of vascular bundles two of which are 

 indicated. Cells containing starch occur around the vas- 

 cular bundle and form a definite starch sheath {st. sh.) to 

 the outside of the latter. The general distribution of the 



