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THE AMEBIC AX NATURALIST [Vol. XLII 



the life history does not depend upon its containing the reduced 

 number. 



2. In Last Ira pst u<lo-mas var. crishila <t pospora apogamy and 

 apospory follow one another in the same manner as described 

 above, but the number of chromosomes (probably 60) is so close 

 to that of the gametophyte in the type species (72) that it seems 

 probable that in this form the sporophyte retains the reduced 

 number (x) of the gametophyte. This condition is exactly the 

 reverse of that noted above showing that the morphology of the 

 sporophyte likewise does not depend upon its containing the 

 double number (2x) of chromosomes. 



3. The third and most striking conditions described by 

 Farmer and Digby refer to a peculiar migration and fusion of 

 nuclei in the cells of the prothallium just before the apogamous 

 development of the sporophytes. These observations are re- 

 corded from the study of two polydactyla varieties of Lastrea 

 pseudo-mas which form their spores with chromosome reduction 

 in the usual manner. The nuclear migrations and fusions occur 

 in the younger regions of the prothallia, in the wings as well as 

 in the thicker portions. A nucleus assumes an elongated form 

 with the pointed end against the wall which it is about to pierce. 

 A pore is formed through which the nucleus slips and makes 

 its way to the nucleus of this receptive cell which usually re- 

 mains rounded. The two nuclei come to lie closely pressed 

 against one another and gradually fuse. Older prothallia thus 

 have fusion nuclei with double the gametophytic number of 

 chromosomes (2x) and the cells of the apogamously produced 

 sporophytes are found to have nuclei of this type ; the authors 

 conclude that they are derived from such fusion nuclei. This 

 process of migration and nuclear fusion, taking the place of the 

 fusion of gametes, finds its analogy in the recent studies of 

 Blackmail and Christman on the rusts. Just previous to the 

 development of the recidia there is an extensive migration of 

 nUClei b * twmi . I1, -^' hl> '" , i»^ so that the cells which give 



which are no longer functional. 



