rust fungi 197 



Phylogeny of the UredinejE (Uredinales) 



In looking for the primitive tA'pes of rust fungi, it has been assumed 

 by some mycologists, that, as the rusts are a specialized group of para- 

 sites, the most primitive forms will be found on hosts which are lowest 

 in the phylogenetic scale of the higher plants. This consideration 

 would place Uredinopsis, which grows upon ferns, as one of the primi- 

 tive rusts, while many of the more advanced tjrpes of Puccinia are found 

 upon the Composit.e. The absence of a germ pore is considered primi- 

 tive, as instance its absence in the aecio-teliospore of Endophyllum. 

 When these first appeared, they were numerous and indefinitely scat- 

 tered, while in the higher rusts, they are reduced in number and 

 restricted to a definite part of the cell wall. The formation and ger- 

 mination of teliospores approaches that of the smuts a more primitive 

 group, hence the formation of a basidium and basidiospores must 

 have been inherited by both from their ancestors. Now among the 

 red algae, such as Griffithsia, the sporophyte bears tetraspores, these 

 develop into a thallus which bears the gametes. Hence one would look 

 for the ancestors of the UREDINE^E among red algae. Again, it has 

 been suggested that the female cells of the aecium have a trichogyne, 

 such as the red seaweeds (Florideae) possess. In the rusts, it has become 

 abortive. 



The ENDOPHYLLACEiE are considered by Grove to constitute the 

 starting point from which the varied forms of the Puccini.ace^ have 

 been derived. In Endophyllum, we have seen that the aeciospore, which 

 is the product of the fusion cell, is also the teUospore from which the 

 basidium and basidiospores arise. The aecium is accompanied by the 

 pycnium here. The first stage of evolution was the separation of this 

 spore form into two: one the aeciospores, germinating like conidio- 

 spores; the other, the teliospore, germinating with the formation of a 

 basidium and basidiospores. PMCcjw/o/iiw suggests these stages. The 

 summer spores are probably modified aeciospores formed as a device 

 for repeating the spore generations without the intervention of another 

 fusion cell. The fusion of the two nuclei in the teUospore is from a 

 cytologic standpoint paralleled by a similar fusion in the BASIDIO- 

 MYCETALES, for a division into four basidiospores follows in both 

 cases, although the mechanism is different. The paired condition 

 of the nuclei found in the ascogenous hj-phae of the ASCOM YCET.ALES, 

 such SiS Pyronema confluens investigated by Claussen (1912), and in the 



