1904] CURRENT LITERATURE "7 
fifteen chromosomes, the ten and twenty being the number characteristic of pure 
pollen mother-cells of the two parents, while the number fifteen is just what one 
would expect in the pollen mother-cells of a genuine hybrid. A recent paper's 
records the results of investigations upon the embryo sac mother-cells of the 
parent and the hybrid. The sporophytic cells of the hybrid always show thirty 
chromosomes. In the pollen mother-cells and embryo sac mother-cells, the 
number of chromosomes is twenty, a very surprising number. These twenty 
chromosomes are not alike, but of two sizes, ten being large and ten small. e 
large chromosomes are evidently double and the small ones single. D. rotundi- 
jolia is represented in the hybrid by ten chromosomes and D. longifolia by twenty. 
In the mother-cell the ten chromosomes of D. rotundifolia fuse with ten of 
D. longijolia, thus leaving the other ten chromosomes of D. longifolia single. 
These are the numbers as seen during the metaphase. The daughter nuclei 
of the tetrads contain quite regularly ten chromosomes, presumably five being 
single and five double. It is evident that these observations have an important 
bearing upon the problem of the reduction of chromosomes, and it is to be hoped 
that the full account of the investigations will not be long delayed.—C. J. Cuam- 
BERLAIN. 
WITH THE rediscovery of Mendel’s laws by Correns, Tschermak, and De 
Vries, there has been a revival of interest in the fundamental problems of heredity 
and hybridization, and many works of both experimental and speculative char- 
acter have appeared. One of the most active workers in this field is Correns. 
In several recent papers he has presented an account of some of his hybridizing 
experiments and has discussed questions of dominance. 
A very striking. result of experiments with Mirabilis hybrids*® was the pro- 
duction of characters in the offspring, which were found in neither parent. Thus 
the offspring of dark yellow or pale yellow Mirabilis Jalapa crossed with the pure 
white form, never showed either yellow or white, but all were red or rose-colored. 
In the second generation these red-flowered hybrids gave rise to a whole series — 
of forms, red-striped, white, pale yellow, rose, and red. Similarly M. Jalapa 
of whatever color crossed with M. longiflora (white with a red-violet throat), 
resulted in offspring having violet corollas, differing in the different cases only 
in the intensity of the color. 
n discussing dominance"? he points out that there may be every degree of 
dominance and Suggests that a character be considered dominant if it occur in 
75 to Ioo per cent. of the offspring, and recessive if it occur in o to 25 per cent. 
of the offspring. Characters transmitted to 25 to 75 per cent. are intermediate; 
*S ROSENBERG, O., Ueber die Tetradenteilung eines Drosera-Bastardes. Ber. 
Deutsch. Bot. Gesells. 22: 47-53. pl. 4. 1904. 
16 Correns, C., Ueber Bastardirungsversuche mit Mirabilis-Sippen. Ber. Deutsch. 
Bot. Gesells. 20: 594-608. I902. 
*7 CORRENs, C., Ueber die dominierenden Merkmale der Bastarde. Ber. Deutsch. 
Bot. Gesells, 21°133-147. 1903. 
