Systematic Arrangement. 83 



From a consideration of the distribution of the Uredineae on their host- 

 plants, Dietel 12 has come to the conclusion that the genus Uredinopsis, 

 belonging to the Melampsoraceae, and occurring on ferns, represents the 

 oldest type of the Rusts, and that the P.ucciniaceae may have developed 

 from the genus Melampsora. However that may be, we may assume that 

 the primitive form of this family was one-celled, and 1 therefore the Uromyces 

 type forms the starting-point ; also that the Transition from the one-celled 

 to the two-celled spore as in Puccinia, was the next step in advance. 



The actual evidence of this transition is seen not only in Puccinia hetero- 

 spora, B. and C., where the two-celled spore has not yet become completely 

 established, being mixed with a large number of unicellular spores, but in 

 such forms as Uromyces vesicul&sus, where there are occasional two-celled 

 spores, Fig. 157, U. tricorynes, Fig. 134, and U. politus, Fig. 317. 



Both Uromyces and Puccinia species occur on plants of the most diverse 

 character, and this would seem to indicate that many of the species came 

 into existence before that specialisation had begun, which resulted in the 

 genus Phragmidium, for instance, confining itself to the Rosaceae. 



The principal genera are here arranged according to the nature of the 

 teleutospore, and the diagrammatic representation of the spores will show 

 at a glance the peculiarities of each : 



1. Uromyces, Link. Teleutospore one-celled, with single germ-pore, 



and solitary on its stalk. Uredospores echinulate or warty all 

 over. Fig 16. 



2. Hemileia, Berk and Br. Teleutospore one-celled as in Uromyces, 



but uredospore smooth on one face. 



3. Uromycladium, McAlp. Teleutospore one -celled as in Uromyces. 



but the sporophore branching toward the apex produces either one 

 spore with a colourless sterile spore or cyst, or two or more spores 

 with or without a cyst. Fig. 17. 



4. Puccinia, Pers. Teleutospore two-celled, with transverse septum 



and with only one germ-pore in each cell. Fig. 18. 



5. Gymnoconia, Lag. Teleutospore as in Puccinia, but aecidia without 



pseudoperidia. 



6. Uropyxis, Schroet. Teleutospore bicellular as in Puccinia, but each 



cell with two or more germ-pores, and the teleutospore membrane 

 consisting of more than two layers. Fig. 19. 



7. Diorchidium, Kalch. Teleutospore two-celled, with longitudinal 



septum and germ-pore at apex of each cell. Fig. 20. 



FIG. 16. FIG 17. FIG. 18, FIG. IP. FIG 20. 



8. Gymno sporangium, Hedw. Teleutospore two-celled (rarely three 



to five celled), and walls which ultimately form a common gela- 

 tinous mass, with usually several germ-pores in each cell. Fig. 21. 



9. Hapalophragmium, Syd. Teleutosp :>re three celled, and consisting 



of two basal cells alongside of each other, with a third on top. 



Fig. 22. 



10. Triphragmimm, Link. Teleutospore three-celled, and consisting of 

 basal cell supporting two others alongside of each other. Fig. 23. 



