390 CLASS BASIDIOMYCETEAE 



into the basal portion of the aecial primordium where dicaryon or pluri- 

 nucleate cells give rise to the chains of spores. In a later paper Miss Allen 

 (1933c) showed that in Puccinia sorghi Schw., whose aecial stage is pro- 

 duced in species of Oxalis, the paraphyses extending from the ostiole of 

 the spermogonium are receptive hyphae as was demonstrated for P. 

 helianthi Schw. by Craigie. The union of sperms to these paraphyses and 

 the actual passage of the sperm nuclei into them w^as illustrated. In her 

 work on P. iriticma and more particularly on P. graminis she reported 

 that receptive hyphae may emerge from stomatal openings or from be- 

 tween epidermal cells in addition to the spermogonial receptive hyphae. 

 Pierson (1933) and Buller (1938) demonstrated the presence of slender 

 flexuous nonseptate receptive hyphae growing up from the base of the 

 spermogonium and out into the drop of spermogonial nectar in Cronartium 

 ribicola Fischer and Puccinia graminis Pers., respectively. When a drop 

 of mixed nectar is added sperm cells were found attached to these hyphae 

 within a few hours. In the latter of the foregoing species there are in the 

 spermogonium paraphyses in addition to the flexuous hyphae but in no 

 case did Buller find that they served as receptive hyphae. (Fig. 129.) 



Just how the sperm nuclei reach the primordium of the aecium is still 



a matter of controversy. Miss Allen (1933a) suggested that they passed 



into the receptive cells which elongated inward and formed a mycelium 



which grew down to the basal portion of the aecial primordium. In Me- 



lampsora lini (Pers.) Lev., where no receptive hyphae are present either 



piercing the epidermis or passing through the stomata or emerging from 



the spermogonia she reported (1934a) that the sperm cell dissolves a hole 



through the outer epidermal wall of the host {Linum usitatissimum L.) 



through which it gains access to the lumen of the cell where it germinates 



or through which a slender germ tube passes. In either case a slender 



branched mycelium arises which grows toward the aecial primordium 



where abundant pairing of hyphae occurs, resulting in the formation of 



the basal cells from which the chains of aeciospores are produced. The 



suggestion has been made that the sperm nuclei possibly initiate a general 



diploidization of the mycelium of the sorus so that all of the mycelium 



between the point of union of sperm and receptive hypha to the aecial 



primordium is diploidized, as Lehfeldt (1923) and Buller (1930) showed 



to be the case in some of the Eubasidiae. Savile (1939) showed that in 



several rusts investigated by him the cells of this intervening mycelium 



are not diploidized, suggesting that the sperm nuclei travel from cell to 



cell, without accomplishing diploidization, until the aecial primordium is 



reached. He also demonstrated that sori close together in the leaf tissue 



can fertihze one another without intervention of the sperm cells, probably 



by contact of the mycehal cells and mutual diploidization. Andrus (1933) 



obtained differential staining of the sperm nuclei and of those of the 



