256 GENETICS [BoT. Absts., Vol. X, 



ately so, and 347 were rust-free, — approximately a 1: 2:1 ratio. The genotypes of some of 

 the F2' plants were tested by growing the F3 plants. Taking the whole F2 crop after adjust- 

 ment with the F3 results, the following composition was indicated: 392 homozygous sus- 

 ceptible, 797 heterozygous susceptible, and 371 homozygous immune. Different behavior in 

 different years is attributed to the operation of environmental factors. — Armstrong's pre- 

 liminary studies with wheat indicate that resistance to mildew (Erysiphe graminis) behaves 

 as a Mendelian dominant. — A. N. Wilcox. 



1688. Brumpt, E. Recherches sur le determinisme des sexes et de devolution des Anguil- 

 lules parasites (Strongyloides). [Studies on the determinism of sex and the evolution of the 

 parasitic Anguillula (Strongyloides).] Compt. Rend. Soc. Biol. 85: 149-152. 1921. — Strongy- 

 loides papillosus, parasitic in the small intestine of sheep, exists in a parthenogenetic parasitic 

 generation and a free-living bisexual generation. Eggs laid by the parasitic form pass with 

 the feces and produce rhabditic larvae, of which some develop directly into strongyloid larvae 

 ready to infect a new host, some into males and females. The bisexual generation is mostly 

 sterile because of rarity of males. Cultures usually contain 1 male to 1000-2000 females, 

 rarely a much higher proportion. The proportion of directly developing strongyloid larvae 

 and of adult males varies; in many cultures development is exclusively direct, most others 

 show 95-98 per cent direct development, and a few show as high as 90 per cent indirect devel- 

 opment (males or females). — From the feces of young infected rabbits there were recovered 

 237 males, 409 females, 1236 direct larvae, and later many larvae of indirect cycle coming 

 from fertilized females. The higher proportion of indirect development and of males in 

 rabbits than in sheep is attributed to the physico-chemical character of the intestinal mucus. 

 A strongyloid infectious larva from a parthenogenetic parent will, if reared in a rabbit, yield 

 a parthenogenetic animal whose eggs produce 1000-2000 times as many males as if the stron- 

 gyloid larva had been reared in a sheep. — A. Franklin Skull. 



1689. Castle, W. E. An improved method of estimating the number of genetic factors 



concerned in cases of blending inheritance. Science 54: 223. 1921. — A modified formula for 



estimating the number of genetic factors (n) concerned in cases of blending inheritance (see 



D2 . . . 



following entry) suggested by Wright is n = — ^ ^, in which D is the difference between the 



80-2— <7- 



means of the parental races, o-i the standard deviation of the Fi, and a 2 the standard deviation 



of F2. — D. F. Jones. 



1690. Castle, W. E. On a method of estimating the ntunber of genetic factors concerned 

 in cases of blending inheritance. Science 54: 93-96. 1921. — The amount of variability of F2 

 over Fi, shown by the standard deviation, divided by the difference of the 2 parental means 

 is taken as a comparative measure of the number of factor differences concerned in cases of 

 blending inheritance. Applied to data for seed weight of maize, it gives from 11 to 19 as 

 the number of genetic factors involved. In a cross of Polish X Himalayan rabbits 50 or more 

 factors were calculated as governing body size. Serious limitations as to the applicability 

 of this method are recognized, viz., it applies perfectly only to cases in which the parents 

 are genetically pure, and does not allow for unequal effect of different factors. — D. F. Jones. 



1691. Castle, W. E., and W. L. Wachter. Genetics of Hereford cattle. Jour. Heredity 

 12 : 37-39. Fig. 27-28. 1921 .—This is a criticism of a paper by Frances Pitt (see Bot. Absts. 5, 

 Entry 1605), in which an attempt was made to account for variations in the coat pattern and 

 intensity of color of Hereford cattle on the basis of 5 Mendelian factors. The present authors 

 hold that the data are insufficient to demonstrate the unit nature of these factors. — Seivall 

 Wright. 



1692. Clausen, R. E., and T. H. Goodspebd. Inheritance in Nicotiana Tabacum. 

 II. On the existence of genetically distinct red-flowering varieties. Amer. Nat. 55: 328-334. 

 1921. — In studies of inheritance in Nicotiana Tahacum the following formulae were suggested 

 for 4 flower colors: WW RR PP, carmine; WW RR pp, light pink; WW rr pp, red; and ivw 



