U RE DIN ALES 591 



Since plasmogamy took place originally, as in the Polyporales and 

 the Agaricales, anywhere between two hyphal cells, its shifting 

 in the life cycle of the rusts and the remaining cases of pseudogamy 

 are explained. Because of their endoparasitism, the hyphae became 

 limited to the narrow intercellular spaces where they generally found no 

 mate. Hence it is not remarkable that plasmogamy took place (at first 

 preferably and in time exclusively) where for the first time in the life 

 cycle numerous parallel hyphae were pressed together, i.e., in the primary 

 uredinia of the ancestral forms. From these developed the more highly 

 specialized aecia. This derivation is based on the fact that the uredinium 

 possessed both the single-spored type (in which the stipe cells have only 

 one purport) and the chain type, which led directly to the aecia. It is also 

 supported by the fact that in certain heteroecious forms, as Puccinia 

 Sydowiana (P. Vilfae), P. perdermiospora and P. Seymouriana, the 

 aeciospores show peculiarities of structure so similar to those of the 

 urediniospores that Arthur assumes a genetic connection between the aecial 

 mycelium and the uredinial mycelium on other hosts, which he has 

 demonstrated by cultural experiments. According to this, the eu- type 

 would have arisen from the brachy- type. 



In connection with this localized pseudogamy the different groups of 

 copulating hyphae may be explained; the types of Puccinia Mariae- 

 Wilsoni, P. Violae and Endophyllum Sempervivi, etc., are only special 

 cases produced by the structure of their sorus. Where the separating 

 wall is incompletely dissolved or only a pore is formed, plasmogamy is 

 heterogamous; where the dissolution of the wall proceeds further and 

 extends almost along the whole wall, the nuclear migrations become 

 feeble and plasmogamy is isogamous according to the present terminology ; 

 these differences are not fundamental but only quantitative. 



The abscission of sterile cells may be explained on this basis, as Mme. 

 Moreau does. Copulation took place only after the basal cells had already 

 cut off some spores, and had continued their activity as diploconidia. 



From these points of view, one may represent the phylogenetic 

 development of the Uredinales hypothetically in the following manner 

 (Dietel, 1903, 1904, 1909, 1912, 1915, 1918; Faull, 1928): The primitive 

 forms derived from the Auriculariaceae had lived on ferns in the Silurian. 

 When the conifers appeared, its gametophyte could also live upon these. 

 Subsequently the greater part of the cycle was shifted to the conifers upon 

 which it developed greater dependence. They retained the gametophyte 

 host and successively seized as suitable hosts those which, in the course 

 of geological time, they encountered among the developing angiosperms. 

 From a morphological viewpoint, they are characterized by the develop- 

 ment of special zeugites which in the lower forms are formed at any point 

 in the mycelium but in the higher forms arise in special sori and are trans- 

 formed into teliospores. In the Coleosporiaceae and Melampsoraceae, 



