146 BOTANICAL GAZETTE [august 



cell divisions proceed in the cushion region as usual in a normal 

 casCj but no functional archegonium is formed. In a certain portion 

 in or near the cushion region, a superficial cell divides perpendicular 

 to the surface of prothallium, while cells below the surface divide 

 in various directions. Thus a mass of peculiar structure, whose 

 further development would result later in an independent sporophyte, 

 is worked out directly by the continuous growth of the prothallium. 



The nuclear conditions were traced through the critical stage, inter- 

 mediate between gametophytic prothallia and sporophytic structure, 

 to the independent sporophyte* The number of chromosomes remains 

 unchanged, always being 64 or 66. There is no migration of a 

 nucleus from a neighboring cell to effect fusion, as is reported in 

 Lastrea. 



Conclusions, — The nuclear condition of Nephrodium moUe may 

 be summarized as follows : 



I. The nuclei of the prothallia contain 64 or 66 chromosomes, 

 the reduced, gametophytic, or x number. The nuclei of the gametes 

 contain the same number. The fusion nucleus in the fertilized egg 



chromosomes 



rmg sporoger 

 Nephrodium 



chromosomes 



sporophyte the 2X number, and that sporogenesis and fertilization 

 are the periods which mark the initiation of the two distinct generations. 

 2. The nucleus of a prothallial cell with the :\: number of chromo- 

 somes (64 or 66) sometimes becomes directly the nucleus of a sporo- 



apogamously produced ; so that the x number 



poroph} 



seem to affect the fundamental 



tion of generations is marked by the difference in the number of chromo- 

 somes in the normal life-history; but is simply an abnormal case 

 of secondar}' importance. Still it must be admitted that in the case 

 of apogamy at least the number of chromosomes is not the only factor 

 which determines the character of the sporophyte and gametophyte. 



The University of Chicago 



