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I 



1907] CHRISTMAN— MORPHOLOGY OF THE RUSTS 85 



portion of the ^^basidium'^ which contains the two nuclei is separated 

 off by a wall. Richards' obser\^ations on nuclear behavior are of 

 rather uncertain value, since he believed that all parts of the aecidium, 

 including the vegetative mycelium, contained binuclcated cells. He 

 describes the same general method of aecidium-formation for the 

 aecidia on Houstonia caeriilea and Ranunculus septenlrionalis. The 

 process here described shows a marked resemblance to that found 

 by Massee. There is a large hypha^ which may be the outgrowth 

 from a sexual cell or may have so originated in the ancestors of the 

 rust. 



INIaire (16), in 1900, found in Endophyllum s em pervivi Alb. & 

 Schw. that the vegetative hyphae consist of uninucleated cells to their 

 very ends in the base of the aecidium. These end cells, however, 

 enlarge and become binucleated by a nuclear division unaccompanied 

 by a cell division. Upon this binucleated end cell the spores are 

 borne. Maire holds this process to be quite universal in the aecid- 

 ium. In another paper (17) published about the same time, ^Iaire 

 compares the life-history in the Uredineae with that of the mosses 

 and ferns and of cyclops. He sees in the beginning of this binu- 

 cleated phase in the life-cycle the change from gametophyte to sporo- 



phyte, and in the fusion of the nuclei in the teleutospore a ^^mixie," 

 while in the germination of the teleutospore and in the promycelium 

 there occur the reduction divisions. The doctrine of alternation of 

 generations in the development of the rusts, while opposed in essential 

 points to the views of Dangeard and Sappin-Troufey, has found 

 confirmation in the later work of Blackman and myself- 



Blackman (2) in 1 904 was perhaps the first to show that two cells 

 are concerned in the production of the binucleated cell at the base of 

 the row of aecidiospores. In Phragmidium violaceum Wint. he found 

 a series of large uninucleated cells standing vertically beneath the epi- 

 dermis of the host. Each cell cuts oflf a sterile apical cell and then 

 becomes binucleated by the entrance of a nucleus from one of the 

 neighboring vegetative cells. This nuclear migration is accomplished 

 by the smaller nucleus from the vegetative cell penetrating the wall 

 by drawing itself through a small perforation. Blackman terms this 

 cell containing the two nuclei the fertile cell, and from it the row of 

 spores and intercalary cells is produced. Blackman agrees with 



