DEPARTMENT OF EXPERIMENTAL EVOLUTION. 139 



TETRACOTYLEDONOUS BEANS. 



Dr. J. Arthur Harris has continued his investigation on variation, 

 correlation, and selective death-rate of garden beans, especially those 

 which have three or four cotyledons. A detailed study of the vascular 

 anatomy of such seedlings, which has been carried on in the last three 

 years with the collaboration of Dr. E. W. Sinnott and Dr. John Y. 

 Pennypacker, will shortly be ready for publication. 



HEREDITY OF COLOR IN DOGS. 



A study has been made of data derived from the studbooks of the 

 American Kennel Club to get at the inheritance of color in three breeds 

 of dogs — Great Danes, Dachshunds, and Pomeranians; and a paper 

 based on the data on Great Danes, written by Miss E. Elizabeth Jones, 

 who has collaborated with Dr. C. C. Little in this work, is now in press. 

 The follo^Ying color-factors, apparently Mendelian in nature, have 

 been demonstrated: 



(1) H, a factor for "harlequin" (white) spotting, epistatic to its 

 allelomorph h, the factor for solid-colored coat. 



(2) D, a factor for intensity of pigmentation allelomorphic to d, 

 producing dilute coat pigmentation. 



(3) A triple allelomorph series of which the members are in order of 

 dominance: E, a factor for extension of black pigment to the v\^hole 

 coat; E' , a factor for partial restriction of black pigment, producing 

 "brindle" or ' 'tigered" pattern, and e' , a factor producing the "fawn" 

 coat-pattern, in which black is confined to the muzzle, face, and feet. 



(4) S, a factor for self or white coat, allelomorphic to s, a factor 

 producing a white chest or foot spot. 



CROSSING OVER AND NON-DISJUNCTION IN SEX-LINKED TRAITS IN CATS, 



DOVES, AND CANARIES. 



Dr. Little has reviewed the available literature to determine how 

 completely the facts of inheritance in cats, doves, and canaries agree 

 with the hypotheses of crossing over and non-disjunction advanced by 

 various investigators to explain the occurrence of exceptional color 

 classes in these animals. 



In cats it was found that the exceptional color varieties were of two 

 distinct sorts: (1) those which involved merely the appearance of an 

 entirely normal and common color variety in a cross in which it was not 

 expected, and (2) tortoise-shell males, which are an extremely rare 

 variety, usually sterile, appearing irregularly, and, when they are 

 fertile, breeding as yellows. 



The exceptions in doves and canaries fall in the first of the two 

 categories. To explain this first category, "crossing over" and 

 "non-disjunction" meet serious difficulties, in that they predicate the 

 appearance of color classes not yet observed, or interchange of genes 



