vni] UREDINALES 217 



in the germination of which the sporophyte comes to an end and the new 



gametophyte is initiated. 



Intci this simple life-history the nredospore and aecidiospore are held to 

 be afterwards successively inserted as extensions of the sporophytic phase. 



From such a point of view the rust might be related directly to the 

 Phycomycetes or other simple forms. 



Blackmail's work, on the other hand, indicates that the spermatium is 

 an abortive male element, the fertile cells of the aecidium are female organs 

 which, in the absence of normal fertilization, either fuse in pairs or receive 

 a vegetative nucleus by migration. In micro- forms the female organs have- 

 disappeared and the abbreviated life-cycle, like that of the pseudapogamous 

 ferns, shows the sporophyte initiated by an association of two vegetative 

 nuclei. The eit- forms (or the -opsis forms with teleutospores, aecidiospores 

 and spermatia), are therefore primitive and the forms with a shorter life- 

 history are of secondary origin and reduced. The female organ consists of 

 two cells, the upper of which may have functioned as a trichogyne. 



Comparing the two hypotheses it may be noted that Blackmail's has 

 the advantage of correlating all the known facts, since the association of 

 female nuclei in pairs and of female and vegetative nuclei are both observed 

 methods of replacing normal fertilization. Christman, on the other hand, is 

 obliged to ignore the migrations of vegetative nuclei, or to regard them as 

 pathological. Even for this reason alone it would appear, in the present state 

 of our knowledge, more probable that the Uredinales are a group in which 

 the normal sexual process has disappeared, and is replaced by various forms 

 of pseudapogamy. The young aecidia must then be regarded as groups of 

 female organs, each consisting of a fertile and a sterile cell, and the sper- 

 mogonia would appear to be corresponding groups of male organs, the 

 spermatia or antheridia, with the filaments which bear them. 



A third suggestion proposes Endophyllum as a primitive form. The 

 mycelium of uninucleate cells bears spermatia and cluster-cups. At the 

 base of the cup fusion of fertile cells in pairs occurs, and spores and inter- 

 calary cells are produced in chains. The spore germinates by the formation 

 of a septate basidium on which four Imsidiospores are produced in E. 

 Euphorbiae, but an irregular number, sometimes as many as eight from one 

 cell, in E. Sempervivi. 



In Uromyces Cunninghamianus (on Jasiiiiiutiii) Barclay, in 1 So 1 , observed 

 that the aecidiospore germinates by a tube in which one transverse wall is 

 formed and the cells give rise to secondary hyphae which produce infection. 

 On the resultant mycelium, spores similar in arrangement to aecidiospores 

 are formed; so that here, as in Coleosporium, we have the accessory spores 

 of the diplophase produced in chains. In the same sorus teleutospores, 

 which are in this genus unicellular, may also arise. The cytology of this 



