66 BOTANICAL GAZETTE [JULY 
is reached that the definitive chromosomes of the first mitosis constitute two 
branches which are variously placed with relation to each other. These two 
branches are the daughter chromosomes of the first mitosis. During the meta- 
phase or anaphase these daughter chromosomes split longitudinally. In the 
telophase no complete spirem is formed nor do the nuclei reach the resting 
condition, but the chromosomes preserve their individuality so that the longi- 
tudinal portions which appeared in the anaphase of the first mitosis become the 
daughter chromosomes of the second mitosis. Consequently, the second mitosis 
cannot be a reduction division. Whether a reduction takes place at the first 
mitosis will be discussed in the second memoir. In the general résumé the 
conclusion is reached that in both plants and animals the definitive chromo- 
somes of the first mitosis, at the equatorial plate stage, are composed of two 
continuous branches. There are two categories of theories as to the significance 
of the second mitosis, the one holding it as an equation division and the other 
as a reduction division. 
In regard to the two constituent branches of the chromosomes of the first 
mitosis, there are two possibilities: if they are longitudinal pieces of a segment 
of a primary chromosome, the heterotypic division is an equation division; if, 
on the other hand, each of the two branches is a complete somatic chromosome, 
there is a true reduction in the WEIS MAN sense. The important question is, 
How are the chromosomes of the first mitosis formed? This will be the subject 
of the second memoir. 
The work will be welcomed by cytologists, for the subject matter is well 
arranged and conflicting theories are impartially discussed. While the title 
indicates only a critical review of the literature, the work is something more, 
because so much botanical investigation has been done in the writer’s own lab 
oratory, and because even the zoological section has not been written entirely 
from the literature, but from the writer’s own preparations and numerous prepa 
rations loaned by prominent investigators of animal cytology.—CHarLEs J. 
CHAMBERLAIN. 
Nova in hybrids.—As has been already noted" in these pages, TSCHERMAK 
found a large number of instances in which nova appeared in hybrid beans and 
peas, in very definite ratios which were readily related to the ordinary Mende- 
lian ratio. These nova were explained by him as characters latent in one of 
action of two or more pairs of units, the positive member of some or all but one 
of these pairs of units being invisible because of the absence of the other mem 
ber of the combination. For example, an albino mouse bred with a brow? 
mouse may produce black offspring, because the albino contains a unit which : 
8 See Bor. GAZETTE 39: 302. Apr. 1905. 
9 See Bor. GazETTE 40: 234. Sept. 1905. 
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