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THE AMEBIC AX NATURALIST [Vol. XLIV 



fusions seem probably to be present in all rusts which 

 have an aecidium or primary uredo and may occur in two 

 forms involving in the one case merely the migration of a 

 nucleus into a so-called fertile cell which then develops 

 into the chain of aecidiospores, while in the other case 

 there may be a complete cytoplasmic union of equivalent 

 cells the so formed binucleated fusion cell then develop- 

 ing into a row of aecidiospores or a series of primary 

 uredospores. 



Dangeard and Sappin Trouffy discovered that the 

 binucleated cells in the rusts originate with the ax?idiuni, 

 but the real significance of the binucleated condition and 

 the method of its origin first became clear with the work 

 of Blackman, Christman and Olive. 



It is quite probable, as Blackman maintains, that these 

 fusing cells in the aecidium of the rusts have been much 

 modified from the ancestral conditions of the sex cells of 

 the group, so that their fusion is to be properly charac- 

 terized as a vegetative fertilization. Still there can be no 

 question that functionally these are sexual unions, and we 

 can hardly imagine anything more illuminating as to the 

 relations of the male and female pronuclei in the cells 

 produced by fusion and hence containing the double 

 chromosome number. There can be no question here 

 that the male and female chromosomes maintain their 

 independence throughout the entire sporophytic life cycle 

 and that nuclear fusion and synapsis are two closely as- 

 sociated phases of that more intimate union of the chro- 

 mosomes which the behavior of hybrids suggests must 

 occur at the close of the sporophyte. Such a series of 

 binucleated cells is unknown among animals but the tend- 

 ency to persistent independence shown by the pronuclei 

 in the embryonic development of Cyclops shows that 

 there is every reason for believing that here and prob- 

 ably in all nuclei with 2n chromosomes the hereditary 



quite the same physical independence throughout the 

 sporophyte as is so convincingly shown in the rusts. 



