214 



GENETICS IN RELATION TO AGRICULTURE 



Shull's conclusions are further supported by evidence from the 

 inheritance of a sex-linked character in Lychnis, the only sex-linked 

 character thus far known in plants. The character in question is that 

 of narrow rosette leaves as distinguished from the normal broad type of 

 leaf, and there are other associated character differences (Fig. 96) . The 

 narrow-leaved form, called angustifolia, was discovered by Baur as a 

 single male mutant individual, a significant fact when taken in connection 

 with its subsequent behavior. The factors in this case are B for the 

 broad-leaved condition and 6 for the narrow-leaved condition. Crosses 

 between typica females (BX)(BX), and angustifolia males (bX}Y 



Fio. 96. Adult rosettes of Lychnis dioica; OH the left a plant of the normal form, typica; 

 on the right a plant of the narrow-leaved form, angustifolia. (After ShuU.) 



gave in F\ all broad-leaved plants (BX) (bX) females and (BX) Y males. 

 Heterozygous broad-leaved females (BX)(bX) mated to broad-leaved 

 males (BX)Y gave all broad-leaved females, and approximately equal 

 numbers of broad-leaved and narrow-leaved males. Hermaphrodites 

 were also found to behave the same way with respect to the factor B 

 as did the males, which confirms the hypothetical relation supposed to 

 exist between hermaphrodites and females. The evidence clearly 

 indicates the existence of sex-linkage of the kind called for on the assump- 

 tion that Lychnis exhibits the XY type of sex-inheritance. 



Secondary Sexual Characters. Secondary sexual characters are 

 those which appear as an invariable or almost invariable accompani- 

 ment of a particular sex in most animal forms. They include many 

 diverse things, such as the antlers in male deer, the horns of the males of 

 some breeds of sheep, the mane of the lion, the power of song of many 



