CHAPTEB III 



SPORE FORMS OF THE UREDINALES 



/ECIDIUM. 



. Kcidia are usually of a cup-like shape, partly embedded in 

 the host, and with the free protruding edge more or less 

 recurved. This is the typical and presumably the most highly 

 evolved form. In it the spores are at first completely enclosed 

 li\ a firm structure, the peridium, the cells of which have the 

 membrane thickened on the inside wall or the outside or both, 

 ami arc arranged in very definite rows like the spores. Bu1 

 there are a number of variations on this type, most, if not all, 

 of which belong to a lower stage of evolution. Sometimes the 

 peridium has the cells less definitely arranged in rows, and 

 i herefore opening more irregularly ; at other I hues the peridium 

 is thin-walled and delicate, and in that case it usually opens by 

 a rounded pore and the edges do not roll back. In Hyalopsora 

 and its allies such a peridium is formed round the uredo-sori, 

 and there are reasons for believing that in these cases the pore 

 arises just beneath a stoma. A still simpler stage is represented 

 by those cases where there is no definite peridium at all, but 

 merely .-i surrounding circle of paraphyses which in a few cases 

 are almost or even totally non-existent. This is called a Carina 

 and indicates a more primitive form ; it is found in Phragmidium 

 and Melampsora. In the non-British Gymnoconia Peckiana 

 (= Puccinia Peckiana, on Rubus) peridium and paraphyses are 

 both entirely absent. 



Again, if there is a definite peridium, it need not have the 

 .shape of a cup. It may be elongated-cylindrical, straight or 

 curved like a horn : this is called a Roestelia and is confined to 



