No. 463 J STC/DIES ON PLANT CELL— VI. 4.^7 



nuclear plate still grouped in pairs as dyads (bivalent chromo- 

 somes). The details of spindle formation and the heterotypic 

 mitosis do not concern the present discussion of reduction phe- 

 nomena. The reduction has occurred with the formation of the 

 dyads and the mitosis simply distributes the 24 chromosomes 

 (generally called daughter chromosomes) which are believed to 

 be- the morphological equivalents of the sporophytic chromosomes 

 that entered the spore mother-cell from the archesporium. 



Just before the separation of the sporophytic chromosomes 

 during metaphase of the heterotypic mitosis a longitudinal fission 

 appears suddenly in each element extending almost the whole 

 length. This is the second longitudinal fission as interpreted 

 by Gregoire ('99), Guignard ('99), Strasburger (: 00), Mottier 

 (: 03), and others, with whom Allen is in full agreement. It is 

 of course a premature division of the chromosomes preliminary 

 to the homotypic mitosis. The second fission is probably com- 

 pleted at this time but the elements of each pair (formerly 

 called granddaughter chromosomes) remain clinging together at 

 one end by a peculiar overlapping of the hooked tips forming 

 thus a V-shaped pair whose apex is drawn to the poles of the 

 heterotypic spindle. The daughter nuclei following the hetero- 

 typic mitosis are not in a true resting condition and the chromo- 

 somes while forming a spirem show abundant evidence of 

 independent structure. They emerge from the spirem at the 

 prophase of the homotypic mitosis as the same morphological 

 entities (i. e., as V-shaped pairs) and are thus brought to the 

 nuclear plate from which they are distributed generally as fairly 

 straight rods to form the nuclei of the pollen grains. 



.Rosenberg's (:03a, :04a, :04b) studies on the hybrids of 

 Drosera furnish further evidence that the chromosomes from 

 different parents fuse in pairs during the prophase of the 

 heterotypic mitosis. The gametophyte number of chromosomes 

 in Drosera rottmdifolia is ten and in D. longifolia twenty and 

 those of the former species are larger than those of the latter. 

 The sporophyte number in the hybrid is thirty as would be 

 expected. At the heterotypic mitosis of sporogenesis, however, 

 twenty chromosomes appear in the hybrid, half of which are 

 plainly double structures and consist each of a larger and a 



