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1007] CHRISTMAN^MORPHOLOGY OF THE RUSTS 83 



empty and dwindled, while the oogonium became large and dense 

 . and nodules budded out upon its surface. These nodules elongated 

 and formed the ^^basidia" from which the rows of aecidiosporcs are • 

 abstricted. Those nodules formed near the base of the oogonium 

 produced the peridium. Before the fusion he finds in the oogonium, 

 on staining with methyl green, a well-defined nucleus. After the 

 union with the antheridium, Massee observed several small nuclei 

 in this organ. As to the nuclei of the nodules he gives us no data. 

 This account of the origin of the aecidium would lead naturally to 

 the conclusion that the aecidium cup is a unit structure arising from 

 a single fertilization. In that respect it would be perfectly comparable 

 to the ascocarp. 



Rosen (23) in 1892 gave quite a different account of the forma- 

 tion of the aecidium in the case of Uromyces pisi Pers. In this form 

 the end cells of the hyphae which bear the spores become much 

 enlarged and at first contain one nucleus. This divides and the two 

 so formed lie in the vertical axis of the cell. The one nearer the apex 

 of this '^basidium" divides to form two, and the portion of the cell- 

 containing them is separated off by the formation of a wall. This 

 leaves the "basidium'' containing one nucleus and the process may 

 be repeated. Rosen gives no account of a central organ from which 

 the hyphae bearing the "basidia'^ arise. In the absence of such an • 

 organ the argument that the cup is the unit structure loses force. 

 This would be even more markedly true if the same account of spore 

 formation were found true for the aecidia of the caeoma type. 



A year later Dangeard and Sappin-Trouffy (7) published an 

 account of work done on the aecidia and also the teleutospores of 

 various rusts. They interpret the fusion of the nuclei occurring 

 in the teleutospore as being a fertilization and give to the process 

 the name pseudojecondation. They regard the mature teleuto- 

 spore as a fertilized egg and attach little significance to the origin 

 of the binucleated condition. Sappix-Trouffy also made some 

 observations upon the spore-formation in other stages of the rusts. 

 In the teleuto pustules of Gymnosporangium sahinae he found that 

 one of the two nuclei of the ''hymenial cell" enters the bud. A 

 wall separates the bud from the basal cell; after which the single 

 nucleus divides. These two nuclei now lie side by side in the bud 



