370 
Journal of Agricultural Research 
Vol. VII, No. 8 
The measurements for the Belgian mares are those given by Von 
Nathusius (6). The inheritance is what is usually called blending, but it 
was shown by Detlefsen (i) and others that such back crosses with appar¬ 
ently blending inheritance are susceptible of a Mendelian interpretation, 
on the basis of multiple factors incompletely dominant. If this interpre¬ 
tation of Landman's data (4) is correct, then heavy-horse types may con¬ 
tain factors for lighter bone. The heavy but heterozygous Gudbrandsdal 
horses may well give light cannon bone, for their history shows the infu¬ 
sion of much light-horse blood. The writer hesitates to advance the ten¬ 
tative hypothesis that segregation of size factors in horses may be influ¬ 
enced by age, but some such hypothesis is necessary to account for 
the poor performance of older stallions when compared with young. 
Race-horse stallions have been known to give excellent results when 
very old, for they are not bred for the dominant heavy-bone characters. 
Draft horses of the Gudbrandsdal and other heavy-horse breeds have not 
given similar satisfactory results. The reason may lie in the possibility 
that older stallions and mares are responsible for more recessives, 
whereas the’younger give more dominants. Any such hypothesis, how¬ 
ever suggestive, must be recast in the light of future investigations. 
LITERATURE CITED 
(1) DETl,EFSEN, J. A. 
1914. Genetic Studies on a Cavy Species Cross. 134 p., 10 pi. (1 col.), tab. 
Washington, D. C. (Carnegie Inst. Washington Pub. 205.) Bibli¬ 
ography, p. 129-132. 
(2) Emerson, R. A., and East, E. M. 
1913. The inheritance of quantitative characters in maize. Nebr. Agr. Exp. 
Sta. Research Bui. 2, 120 p., 21 fig. Literature cited, p. 118-120. 
(3) Jensen, J. 
1887. Nogle Forhold, der have Indflydelse paa Nedarvingsevnen hos Hesten. 
In Tidsskr. Landokonom., R. 5, Bd. 6, Hefte 3/4, p. 234-256. Discus¬ 
sion, p. 256-272. 
(4) Landmann, Adolf. 
1914. Die Zucht eines schweren Arbeitspferdes in der Provinz Ostpreussen. 
In Kiihn Arch., Bd. 4, p. 137-293, 11 fig., 2 pi. 
(5) MacDoweix, E. C. 
1914. Size Inheritance in Rabbits, with a Prefatory Note and Appendix by 
W. E. Castle. 55 p., illus. (Carnegie Inst. Washington Pub. 196.) 
Bibliography, p. 47-49. 
(6 ) Nathusius, Simon von. 
1912. Messungen an 1460 Zuchtpferden und 590 Soldatenpferden . . . 247 p. 
Berlin. (Arb. Deut. Landw. Gesell., Heft 205.) 
(7) OettingEn, B. von. 
1908. Die Zucht des edlen Pferdes in Theorie und Praxis. 639 p., 1 pi. Berlin. 
(8) Philips, J. C. 
1912. Size inheritance in ducks. In Jour. Exp. Zool., v. 12, no. 3, p. 369-380. 
(9) - 
1914. A further study of size inheritance in ducks with observations on the sex 
ratio of hybrid birds. In Jour. Exp. Zool., v. 16, no. 1, p. 131-148. 
