ipoS] YAMANOUCHI—SFOROGENESIS IN NEPIIRODIUM 21 



described by Farrier and Moore (17, 18, 19), Gregory (26), 

 Farmer and Shove (20), Mottier (34), and Schaffner (41). 



Consequently, the reduced number of chromosome segments of 

 the heterotypic mitosis in Nephrodium are not two sporophytic 

 chromosomes joined end to end, which come to hV side by side by 

 the approximation of the arms of the looj« and break apart at the 

 head of the structure; but they are bivalent chromosomes or pairs 

 of sporophytic chromosomes derived from the two threads of the 

 synaptic stage that are always in close association side by side from the 

 beginning^ as claimed by Allen, Berghs^ and Gregoire. 



Results obtained by Miyake (32) in a number of monocotyledons 

 and by Overton (36) in a number of dicotyledons accord in general 

 "with this description of the mode of formation and separation of 

 heterotypic chromosomes. 



Although the present account of Nephrodium differs widely from the 

 accounts of Farmer and Moore, Gregory, Stevens, and Str.\s- 

 BtTRGER in the interpretation of the s}"napsis and the prophase of 

 heterotypic mitosis, yet it agrees in one fundamental pointy namely, 

 that the fct division is heterotypic and separates whole sporophytic 

 chromosomes. 



HoMOTYPic DIVISION- — That the chromosomes in the second 

 division in Nephrodium divide longitudinally is in accordance with 



the vesretative mitosis 



an essential pomt 



difference betw^een the two cases^ namely, in \egetative mitc^is the 

 resting stage is always intercalated between the diromosomes in the 

 last telophase and those of prophase of the ensuing division, so that 

 each mitosis is followed by a resting stage, and a line of new longitu- 

 dinal fission of the chromosomes arises in the early prophase of each 

 division; while in the homotypic mitosis no restipg nucleus is formed 

 in telophase of the preceding mitosis, and therefore the homotypic 

 mitosis should not be regarded as a complete (me, standing by itself. 

 Really an early part of the prophase of the second divfeion may be 

 regarded as beins: initiated at the fij^t divisicm, because the homotypic 



mitc^is separates two daughter halves of a single sporophytic chromo- 

 some of the first di^-ision: the partial ionsitudinal fission of this sporo- 



-e- 



phytic chromosome was begun during the anaphase of the first mitc^is 

 although the fission w^as obliterated in the last telophase. 



