1922] CURRENT LITERATURE 155 
to produce a hybrid which contains 24 chromosomes from parent A and 24 
from parent B. Reduction division by this hybrid should produce gametes 
of numerous types, ranging from those which would possess the 24 chromo- 
somes of the A parent and none of the B chromosomes, to the other extreme in 
which the reverse would be true. It is assumed that gametes in the inter- 
mediate condition, with a liberal mixture of A and B chromosomes, fail to 
develop. “Any gamete containing elements derived from both systems would 
give a reaction system subject to profound disturbances incident upon the 
inharmonious relations set up” between the A and B elements. In consequence 
the only gametes which successfully develop are such as contain all or almost 
all of the A chromosomes, or all or almost all of the B chromosomes. This 
hypothesis of selective survival of the gametes produced by the F, species 
hybrid is supported by the following very striking facts. Back crosses with 
either parent result in the production of a relatively much higher number of 
forms identical or almost identical with that parent than would otherwise 
be expected. Also, in the scanty F, generation which it is sometimes possible 
to obtain, many more individuals appear which are identical or almost identical 
with a hades grandparents (A and B) than would otherwise be expected. 
rranges the species of Triticum in three groups, characterized 
by baat: chromosome numbers of 7, 14, and 21 respectively. Crossing within 
the groups produces fertile hybrids, but crossing between the groups results 
in more or less sterile hybrids. It is noteworthy that the F,; endosperms are 
well developed in the fertile crosses, but shriveled in those crosses which are 
to produce sterile or partially sterile F; plants. In all cases, however, hybrid 
vigor appears in the vegetative parts of the F,; plants. Evidently endosperm 
development as well as gametogenesis is sensitive to the disturbances resulting 
from the union of “‘inharmonious” gametes. The F, results of Sax,’ however, 
appear not to agree with the ideas of the other investigators, since in this 
generation no greater sterility appears in the intermediates than in the segre- 
gates resembling the grandparents. Ecologists as well as geneticists will 
be interested in the natural law which is suggested by this work of Sax. Ina 
group of species of which the chromosome numbers vary in multiples of an 
original a —: adapta * re Sees with nr chromosome count. 
Thus the eats a ble, and the 7 chromosome 
wheats are fe least cdaptahiacooil C. Courter. 
usarium resistant cabbage.—The selection of Fusarium resistant strains 
of pekeseg is being continued at the Wisconsin Experiment Station by JoNEs? 
7Sax, Kart, Sterility in wheat hybrids. I. Sterility relationships and endo- 
sperm development. Genetics 6:399-416. 1921. 
*Sax, Kart, Chromosome relations in wheat. Science 54:413-415. 1921. 
9 Jones, L. R., WALKER, J. C., and TispALe, W. B., Fusarium resistant cabbage. 
Wis. Agric. Exp. Sta. Res. Bull. 48. 1-34. figs. 10. 1920. 
