164 Vererbung, Variation, Mutation. 



hypothesis, which needs confirmation, is given. If B is a positive genetic dif- 

 ference (or factor) which the Velvet bean lacks, but which is present in the 

 Lyon, Yokohama and China; and C is another genetic factor, present in the 

 Velvet bean, but absent in the other three; and both B and C (either Single or 

 double) are needed for the production of typical stinging bristles; then in the 

 second generation, (1) the stinging plants have both the factors B and C, Single 

 or double, (2) The downy plants have only the factor B, Single or double; 



(3) The long black and "Velvet" plants have only the factor C, single or double; 



(4) The smooth black plants have neither B nor C. If D is a genetic factor, pre- 

 sent in the Lyon and Yokohama, but absent in the Velvet bean, which factor, 

 in the absence of B, causes the formation of black tomentum all over the plant; 

 if between factors C and D there is a partial repulsion, so that they rarely enter 

 the same gamete; then, (1) Plants with neither C nor D will be very rare in F 2 ; 

 (l) Plants with both C and D will be about twice as numerous in F 2 as plants 

 with only C; most of the former will have single, and most of the latter double 

 factors; (3) Plants with D only will mostly have this factor double, and will be 

 about half as numerous as plants with both C and D. We have then for the se- 

 gregation in F 2 : (l) Nine-sixteenths, stinging plants, all with B and C, about 

 two-thirds with D (mostly single), and about one-third without D; (2) Three- 

 sixteenths, downy plants, all with B, and nearly all with D (mostly double): 



(3) Three-sixteenths, plants with long tomentum, all with C, about two-thirds 

 (long black) with D (mostly single), and about one-third ("Velvet") without D; 



(4) Nearly one-sixteenth, smooth black plants, without B or C, all with D (mostly 

 double). A very few, recessive downy plants, without B, C, or D. Pearl. 



398) Cook, 0. F., Reticular Heredity. In: Jour. of Heredity, Vol. V, No. 8, 

 S. 341-347, Aug. 1914. 



According to the author the Mendelian theory of heredity may be described 

 as monogenic because it assumes the transmission of only one set of gens or 

 character-units in each germ-cell. A polygenic theory is required to account for 

 the fact that latent or suppressed characters are transmitted, as well as those that 

 are brought into expression. The polygenic nature of heredity is also indicated 

 by the fact that mutative changes of expression usually affect many characters 

 at once, instead of a single characters. A further advantage of the polygenic con- 

 ception is that it allows characters to be brought into analogy with ancestral 

 lines that form the network of descent of the species. The assumption that cha- 

 racters are pre-existent in the protoplasm of germcells as discrete particles or 

 independent units of any sort is not justified by Observation or by logical ne- 

 cessity. Equally convenient and more truly biological methods of thinking about 

 the problems of heredity can be developed by recognizing the relation of here- 

 dity to the network of descent of the species. This conception allows characters 

 to be thought of as representing lines of descent instead of as discrete particles 

 in the protoplasm. Pearl. 



399) Simpson, Q. I., Coat-Pattern in Mammals. In: Jour. of Heredity, 

 Vol. V, No. 8, S. 328-339, Aug. 1914. 



In this paper the author discusses the value to the breeder of hybridizing 

 to obtain particular colors or coat-pattern and how in many cases the genetic 

 composition of animals may be detected by analysis. As illustration the coat- 

 color of various breeds of swine is used. The author states that the white belt 

 of swine might be said to be composed of a single factor, this dominant, and 

 being simply the same factor that can produce a rather low potential of dominant 



