UREDINALES 589 



tion and disappearance of the male organs and by the assumption of their 

 function by vegetative fusions, in the Basidiomycetous line, the female 

 organs disappear first leaving the male organs, no longer functional, as 

 vestigial structures whose presence is still physiologically important 1 

 even after their cells have lost the corresponding female organs with which 

 to copulate. The so-called sexual cells, gametes and sexual fusions are 

 purely secondary, the fusions occurring between cells which are no more 

 homologous to sexual organs, spermatia and oogonia, of any possible 

 ancestral form than are the anastomoses of hyphae of the -f- and — 

 strains of a heterothallic Coprinus. The presence of strains of rusts with 

 a typical two-celled basidium, which is regularly associated with absence 

 of spermogonia and the production of uninucleate spores, suggests that 

 the presence of spermogonia may influence cell fusions in which they do 

 not themselves take part, although a few cases have been observed where 

 uninucleated spores have been produced in the presence of spermogonia. 



There is something in the inheritance of the rusts that determines when and 

 where these cell fusions shall take place, as well as the nature of the cells fusing. 

 The five great orders in the Florideae are distinguished mainly on the basis of the 

 form and disposition of the carpogonial branches and auxiliary cells, and on the 

 nature of the cell fusions which follow as secondary events. The gonimoblasts 

 or ooblastema filaments, sporophytic outgrowths from the fertilized egg, in many 

 genera are also involved in these secondary fusions preliminary to the develop- 

 ment of the carpospores. It is to these secondary cell fusions in which the 

 auxiliary cells of the red alga take the leading part, that we must look for the 

 homologues of the fusing cells of the rust. 



There being no organ such as the egg apparatus in the rusts, the spermogonia, 

 although they are so well developed in many species, can not carry out their 

 primary male sexual function. Nevertheless there may be a series of activities 

 in the growth of the rust linked with or influenced by the very inheritance which 

 manifests itself morphologically in the shape of spermogonia. The fusions 

 between the ooblastema filaments and auxiliary cells, and the other cell fusions 

 in the red algae may very well be determined by the stimulus resulting from 

 the presence of some of that element of maleness normally derived from the 

 spermatium during fertilization. In the absence of the sexual fusions certain 

 auxiliary cell fusions would not occur. Femaleness in the red algae outwardly 

 expresses itself primarily in the organization of the carpogonial branch bearing 

 the egg cell and its trichogyne. Auxiliary cells are secondary manifestations or 

 accompanying phenomena. In a dioecious alga one should not expect to find 

 auxiliary cells borne on the male plant. Femaleness in Caeoma nitens, i.e., the 

 power to develop an egg apparatus, has been lost. Auxiliary cells represented by 

 the cells in the sorus primordium are the secondary expressions. These cells 

 are capable of fusing, usually in pairs, under a certain stimulus. 



1 Unpublished experiments described in a letter from J. H. Craigie confirm this 

 statement fully in Puccinia Helianthi, where the transfer of pycniospores from one 

 pycnium to another appears necessary to secure normal development of aecia and 

 binucleate aeciospores. 



