GENETICS: DAVENPORT AND CONARD 
537 
vidual will throw some light on the nature of the mutation which produces 
quercina. Efforts are being made to secure self-pollinated nuts from 
each of these trees and in 1916 I hope to secure sesqui-hybrids from the 
cross /. calif ornica mut. quercina 9 X 08 HiFiPSc . The completion 
of these breeding tests is especially desirable in view of the diverse be- 
havior of certain of the original quercina trees. One of the type indi- 
viduals breeds true, while a cotype individual produces both quercina 
and calif ornica seedlings and another cotype individual produces nothing 
but calif ornica seedlings. 
The facts reported in this paper may be interpreted in part as meaning 
(1) that the mutation takes place in female flowers only and appears in 
the first generation after the mutation occurs but upon crossing with 
the species type it is completely recessive in the Fi generation; (2) that 
the nature of the mutation is such that only certain genetic factors are 
affected without having the chromosome number disturbed. 
Another walnut mutant has appeared in the form of a laciniate-leaved 
type of Juglans regia. Open pollinated nuts occasionally reproduce 
the new type. It is expected that self- and cross-pollinations will be 
made in 1916 and possibly cytological investigations. 
^Babcock, E. B.. Studies in Juglans I. Study of a New Form of Juglans calif ornica 
Wats., Univ. Cal. Pub. Agr. Sci., 2, no. 1 (1913). 
2Jepson, W. L., in Bnll. So. Cal. Acad. Sci., 7, 23 (1908). 
^Babcock, E, B., Studies in Juglans II. Further observations on a New Variety of 
Juglans calif ornica Wats., and on Certain Supposed Walnut-Oak Hybrids, Univ. Cal. Pub. 
Agr. Sci., 2, no. 2 (1914). 
HEREDITARY FRAGILITY OF BONE 
By C. B. Davenport and H. S. Conard 
CARNEGIE INSTITUTION OF WASHINGTON AND 
GRINNELL COLLEGE. IOWA 
Presented to the Academy, August 30. 1915 
While a weakness or brittleness of the long bones may arise from a 
number of pathological conditions affecting the bones, yet there has been 
recognized for 80 years a constitutional tendency to brittle bone that 
runs through families in such fashion as to demonstrate the presence of 
an hereditary factor. To it has been given the name fragiKtas ossium 
or osteopsathyrosis. 
In a classical case of osteopsathyrosis the femur is frequently found 
fractured at birth, but it mends quickly and smoothly. Repeatedly in 
life a sHght knock causes a bone of the leg or arm to break; and some- 
times before puberty the individual has suffered a score or more of 
