534 SCIENCE PROGRESS 



as observed by him in the ascus, are not incompatible with 

 the view that homologises the ascus with the oomycetous 

 sporangium. He thinks the ascomycetes may possibly have 

 arisen from some phycomycetous group. 



Remarkably interesting work has been done on fertilisation 

 in Uredinese by V. H. Blackman. The cells of the hyphae, as 

 well as the spores in this Order, are binucleate from the mature 

 aecidium stage until the teleutospore is formed, when the two 

 nuclei fuse together. Phragmidium violaceum, with its simple 

 aecidium, was selected for examination to determine at what 

 stage in the life-history of the uredine the binucleate condition 

 arose. It was found that the first hyphae, produced after infec- 

 tion by the teleutospores, had uninucleate cells, and that the 

 cells of the young aecidium were also uninucleate, but at the 

 base of the latter there were present a row of rather large cells 

 termed by Blackman the female cells. These cells become 

 binucleate by the nucleus of a neighbouring cell migrating 

 through the cell wall. The two conjugate nuclei do not fuse — 

 they divide, and a daughter nucleus of each passes on to form 

 the series of binucleate aecidiospores, with the subsequent 

 binucleate mycelium and spores of uredo and teleutospore 

 stages. Fusion between the paired nuclei finally takes place 

 in the maturing teleutospore. Blackman looks on the first 

 association of the two nuclei as a reduced form of fertilisation 

 that came into play as the primary male organs — the spermo- 

 gonia and spermatia — became functionless. He recognises in 

 this life-history an alternation of generations : the gametophyte 

 with single nuclei, represented by the mature teleutospore, 

 sporidia, spermogonia, and mycelium, succeeded by the sporo- 

 phyte which includes all the binucleate stages. Christman, an 

 American investigator, found in another species of the same 

 genus that two of the larger aecidial cells themselves fused, their 

 nuclei remaining distinct. There is evidently no hard and fast 

 rule of procedure, but the end — the binucleate cell — is alwaj^s 

 achieved before spore formation begins. In forms such as 

 Puccinia malvacearum, where no aecidium is formed, the 

 binucleate condition arises just before the formation of the 

 teleutospores ; in other similar species nuclear migration takes 

 place at a very early stage after teleutospore infection. 



The Uredineae have a bad record as disfiguring and destroy- 

 ing rusts. They are all parasites, and form a well-marked 



