No. 463.] STUDIES ON PLANT CELL.— VI. 457 
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 Grégoire (99), Guignard ('99), Strasburger (100), 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 (2. 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, :044, :o4b) 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 een 
in Drosera rotundifolia 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 
