June 9, 1911] 



SCIENCE 



897 



is a dilute form of yellow corresponding in 

 nature to the dilute forms of black and brown. 

 A very simple and direct test of this matter 

 is obtained by breeding " cream " animals to- 

 gether. 



Cream-colored, like all other shades of yel- 

 low mice, are regularly heterozygous, pro- 

 ducing black or brown pigmented young as 

 well as those which are yellow, the yellows 

 being to the non-yellows approximately as two 

 to one.^ Now if the " cream " condition of 

 yellow is produced by the same factor as the 

 dilute condition of black and brown, the 

 " creams " bred together should produce non- 

 yellow, young all of which are dilute, since, as 

 stated, dilution is recessive in nature. 



Such, however, is not the case. Cream ani- 

 mals mated together produce only cream or 

 light-colored yellow offspring, but the black 

 or brown ' pigmented young which they pro- 

 duce are commonly of full intensity. Ac- 

 cordingly, it follows that the " cream " modi- 

 fication of yellow is different in nature from 

 the dilute modification of black and must be 

 produced by a different factor. 



This fact being established, search was be- 

 gun for a type of yellow which when bred by 

 itself would produce yellows and dilute forms 

 of black and brown. Such yellows should, 

 when obtained, be distinguishable from the 

 intense yellow as well as the " cream" type, 

 and should show on microscopic examination 

 of the hair a condition of pigment reduction 

 equal in amount to that seen in the dilute 

 black or dilute brown forms. 



Such yellows have been obtained. They 

 may be deep red, light cream, or any of the 

 intermediate gradations, but they possess an 

 extremely characteristic washed-out dull ap- 

 pearance, which serves to distinguish them 

 clearly from intense forms, even though these 

 be extremely light colored. 



Since this form of yellow occurs in all the 

 gradations from " red " to " cream," it is ap- 

 parent that it represents an independent form 

 of pigment reduction; and since, unlike the 

 " cream " reduction, it is transferable to black 



= See Science, N. S., Vol. XXXII., No. 833, 

 pp. 868-870. 



or brown, it is safe to class it as the dilute 

 form of yellow. 



The fact that black and brown pigment is 

 present in agouti animals in a presumably 

 constant degree of intensity and that the yel- 

 low pigment may independently vary in these 

 animals from cream to deep red, may possibly 

 serve to explain the marked variations seen in 

 the type known as intense black agouti 

 (golden agouti). 



A table showing the result of crossing 

 " creams " (light yellow) inter se follows. 



TABLE I 



Parents, "cream" X "cream"; 

 Offspring, "cream" 31, black 10, brown 14. 

 {light yellow) (intense) (intense) 



From Table I. it will be seen that non-yel- 

 low young of a dilute character are not pro- 

 duced by mating cream-colored animals inter 

 se. On the other hand, such young have been 

 produced by dilute yellows crossed inter se, as 

 shown by Table II. 



TABLE II 



Parents, dilute yeUow X dilute yellow; 

 Offspring, dilute yellow 95, dilute non-yellow 52. 



Further, when dilute yellows are mated with 

 dilute non-yellows the non-yellow offspring 

 are all dilute (see Table III.). 



TABLE III 



Parents, dUute yellow X dilute non-yellow; 

 Offspring, dilute yellow 38, dilute non-yellow 37. 



In the foregoing account dark-eyed yellows 

 are alone used in computing the numerical re- 

 sults. Experiments with pink-eyed yellow 

 forms have been conducted, but the data have 

 not yet been tabulated. 



C. C. Little 



May 22, 1911 



DIMORPHISM OF THE GAMETES OF CENOTHERa' 



Professor de Vries^ has brought to light a 



' Bead before the Botanical Society of Washing- 

 ton, May 2, 1911. 



- ' ' Ueber doppeltreziproke Bastarde von CEno- 

 thera biennis L. und 0. muricata L.," in Biolo- 

 gisches Centralblatt, 31: 97-104, No. 4, February 

 15, 1911. 



