86 REPORTS ON INVESTIGATIONS AND PROJECTS. 



hackle, the daughters show the color that their father has. The reason is 

 that this is a character linked with the sex chromosomes and the daughters 

 get their sex chromosome from their father only, while the sons get a sex 

 chromosome from each side of the house. Occasion was taken, in printing 

 these results, to review cases of sex-limited inheritance in birds and to 

 bring all results into accordance with a simplified formula. Dr. Shull has 

 discovered a sex-limited character in his Lychnis cultures — the first case to 

 be observed in plants. Here a narrow-leafed condition is in the ofifspring 

 of hybrids found only in male plants. 



Plants are usually unsatisfactory for the study of sex-limited characters 

 because they are so often hermaphroditic. In some species, however, ^s 

 noticeably in the cockle, Lychnis, males, females, and hermaphrodites occur 

 side by side in the same culture field. The females are usually sharply 

 differentiated from the others, but the males are only extreme cases of abor- 

 tion of female organs in an hermaphrodite. Many sperm, indeed, carry the 

 determiner for hermaphroditism, the others that for f emaleness ; but the 

 eggs ordinarily carry only the determiner for maleness. It now appears, 

 however, that some eggs do carry the determiner for hermaphroditism ; and 

 it was hoped to get a union of eggs and sperm which should be positively 

 homozygous in respect to the determiner for hermaphroditism, that is, should 

 have it double-derived from both parental germ-plasms. Such a product 

 should be the ancestor of a pure hermaphrodite strain. But, so far, Dr. 

 Shull has met with disappointment. Always there arise eggs that do not 

 carry the determiner for hermaphroditism, but femaleness only. 



Usually, we expect that half of the ofifspring in all forms shall be females ; 

 but we know exceptional cases where, as in plant lice and rotifers, female 

 children only are born for many generations. In Lychnis, also, expectation 

 is not fulfilled; for the sex-ratio of the female sex varies all the way from 

 4 per cent to 97 per cent in difiFerent families of large size; and making all 

 counts, it appears that the females constitute about 62 per cent instead of 

 the expected 50 per cent. 



A third study of sex was made by the Director in collaboration with Pro- 

 fessor Arkell, until recently in charge of the New Hampshire experiment 

 station at Durham, with which this station has been cooperating. This 

 study had to do with the horns of sheep. As is well known, in some races 

 (Merinos) the males are usually horned, the females hornless, and this fact 

 has been explained on the ground that the testis secretes a substance (which 

 the ovary lacks) that stimulates the formation of horns. A difficulty lies 

 in the fact that in other races of sheep, as in most sorts, both ewes and rams 

 are horned, and in other races neither sex. So the data gathered from the 

 sheep-breeding experiments of both stations were gone over and it appeared 

 that the facts were not opposed to the conclusion that the horns of sheep 

 likewise are inherited as sex-limited characters. A note was published in 

 Science to that effect, and in consequence of a criticism of this conclusion 



