960 Davis.—A Comparison of the Reduction Divisions of 
Gates and to the writer supposes a doubling of chromosome count in the 
fertilized egg or very young embryo by the division of the chromosomes 
preliminary to a mitosis which failed, however, to effect their distribution. 
It is known that such failures to effect the normal distribution of chromo¬ 
somes may result from irregularities in spindle formation, as in a monaster, 
by which the full set of divided chromosomes is brought together in a single 
nucleus which contains of course the doubled number. There is much 
experimental evidence on the botanical side from the studies of Gerassimow, 
Nemec, Miss Kemp, and others, and also on the zoological side, which 
shows that by various chemical and mechanical treatments mitoses may be 
interrupted at stages in their division, and two sets of divided chromosomes 
brought together again to form a single nucleus with twice the normal 
number of chromosomes. 
It has long been known from the experimental studies of Gerassimow 
(’ 04 ), beginning as early as 1890, that the size of a cell bears a relation to 
the size of its nucleus. By subjecting the filaments of Spirogyra during 
cell division to low temperature, or treating them for a short time to the 
anaesthetic influence of ether, chloroform, or chloral hydrate, he showed 
that the portions of a partially divided nucleus may unite to form a single 
large nucleus, and that the cell increased in size. This line of investi¬ 
gation was later taken up by Nemec in a series of studies on root-tips, 
the results being brought together in his recent work of 1910. When 
growing root-tips are immersed in solutions of certain drugs, chloral hydrate 
being a favourite reagent, partially divided nuclei may be made to fuse, with 
the result that tetraploid (syndyploid) nuclei are formed having double the 
normal number of sporophytic chromosomes. The effect of the reagent is 
to disorganize the achromatic portions of the mitotic figure, or otherwise 
disturb their functions, so that the movement of the divided chromosomes 
towards the poles is arrested, and they are gathered together to form 
a single nucleus. 
Of especial interest is Nemec’s claim that the tetraploid number of 
chromosomes in some cases returns to the normal number by a heterotypic 
mitosis. This view is based chiefly on the peculiar appearances of the 
chromosomes, suggesting the diads and tetrads of the reduction division. 
Strasburger and others, after failing to confirm Nemec’s observations on 
the ‘ heterotypic mitosis have criticized his conclusions on general grounds. 
Miss Kemp (’ll), however, has found in chloralized root-tips of the pea, an 
especially favourable subject, figures very similar to those of the heterotypic 
mitosis, but her interpretations are not those of Nemec. Although the 
chromosomes have the X, Y, and tetrad forms suggestive of the reduction 
division, Miss Kemp believes on good evidence that these peculiarities are 
due to the direct action of the drug. 
The results and the interpretations involved in the investigations 
