ORDER UREDINALES (tHE RUSTS) 391 



vegetative hyphae in the sorus and was able to confirm Savile's suggestion 

 that the former pass through the hyphae without bringing about their 

 diploidization. Apparently there is lacking a standard method of diploid- 

 izing the fertile cells of the aecial primordium. Miss Allen (1932b) has 

 demonstrated that in Puccinia coronata Corda the sperm cells unite 

 abundantly with the receptive hyphae and that mycelium (carrying the 

 sperm nuclei) grows from these down to the primordium. In the latter the 

 union of basal cells, to be described in the next paragraph, rarely occurs. 

 In the case of Puccinia sorghi Schw., whose spermogonia and aecia occur 

 on species of Oxalis, Miss Allen (1934b) reported that functional receptive 

 hyphae occur in the spermogonium, and also project out of stomata. 

 Sometimes sperm cells germinate on the outside of the leaf and the slender 

 hyphae enter the stomata. Within 24 hours after the " spermatization " of 

 a sorus with compatible sperms 60 per cent of the mycelial cells of the 

 mycelium are found to possess more than one nucleus, through rapid 

 division and migration of the sperm nuclei. Six days after spermatization 

 the first aecia set free their aeciospores. 



Prior to the discovery of the active participation of the sperm cell 

 Blackman (1904), Christman (1905, 1907), Mme. Moreau (1913), Colley 

 (1918), and many others described the manner by which the aeciosporic 

 chains are originated. A layer of uninucleate cells in the basal portion of 

 the aecial primordium either shows fusion by twos, the walls between the 

 upper portions of these cells dissolving out, resulting in a binucleate two- 

 legged cell, or nuclei pass from adjacent cells through small pores to form 

 a dicaryon cell. From this by conjugate division of the nuclei and the 

 formation of successive cells comes a chain of aeciospores and disjunctor 

 or intercalary cells. Just how the two sets of uniting cells originated was 

 not made clear by these authors. It is now apparent that the two uniting 

 cells contain respectively a nucleus originating from the sperm and one 

 from the mycelium developed from the sporidium. Wang and Martens 

 (1939) do not believe that "Christman" conjugations at the base of the 

 aecium are the normal mode of diploidization but that it occurs earlier, 

 perhaps as far back as spermatial fusions with one another or with recep- 

 tive cells of the rust. (Fig. 130.) 



From the foregoing accounts it is 'clear that in some and probably all 

 rusts which produce sperm cells they are functional. Furthermore, the 

 same haploid mycelium produces both sperm cells and receptive hyphae 

 so that both male and female structures are present, yet self-fertilization 

 does not occur. Like the condition in Schizothecium (Pleurage) reported by 

 Ames (1932), in A'eiirospora as demonstrated by Shear and Dodge 

 (1927), and in Stromatinia (Sclerotinia) gladioli (Drayton) Whetzel studied 

 by Drayton (1934), two sexual phases are present, each hermaphroditic 

 but incapable of self-fertilization. 



