No. 460.] STUDIES ON PLANT CELL.— V. 249 ' 



binucleate is one of the most interesting problems in this field of 

 botany. This is the point where we should expect to find the 

 remains of sexual organs, if any are present in the higher 

 Basidiomycetes, but it is not likely that they will be found. It 

 seems more probable that the mycelium with the paired nuclei 

 (perhaps sporophytic in character) arises apogamously with a 

 complete suppression of the sexual organs in agreement with such 

 of the Uredinales as have no scidium and the Ustilaginales. 



Blackman's explanation of the history of the paired nuclei in 

 Phragmidium is full of interest. As stated before, he regards 

 the fertile cell which develops a chain of secidiospores, "as a 

 female reproductive cell which undergoes a process of fertiliza- 

 tion " by a union with an adjacent cell of the mycelium and its 

 reception therefrom of a nucleus. The mycelium then which 

 arises with the secidiospore is sporophytic in character and so 

 remains until the fusion of the pairs of nuclei in the teleuto- 

 spores. The male organs of the rusts are the spermogonia and 

 the male gametes the spermatia which are of course now func- 

 tionless so that the "process of fertilization" is through the 

 introduction into the female cell of a nucleus which is not phy- 

 logenetically a male sexual element. Blackman's (:04 a, pp. 

 ; 349-353; :04b) conception of the process as an act of ferti- 

 lization involves some principles which will be briefly outlined. 



Blackman believes for Phragmidium " that the primitive normal 

 process of fertilization by means of spermatia has been replaced 

 by fertilization of the female cell through the nucleus of an 

 ordinary vegetative cell " and regards the process as very similar 

 to the phenomenon reported in the apogamous development of 

 ferns by Farmer, Moore, and Digby (:03), which will be consid- 

 ered presently. Blackman points out that normal processes of 

 fertilization such as we have included under the head of " sexual 

 cell unions and nuclear fusions " do not involve in many forms 

 (probably all types with a sporophyte generation) an immediate 

 union of the chromatin of the sexual nuclei which is known to 

 remain distinct during the first cleavage mitosis in a number of 

 types {e. g., Pinus and some other gymnosperms). So there is 

 nothing in the delayed fusion of the paired nuclei up to the 

 teleutospore that is seriously against his explanation of the "fer- 



