272 Inheritance in the Groundsel 



Additional Note {August 14, 1912). 



Two F^ colonies of the cross lanuginosus x praecox of 213 and 215 

 plants respectively were raised during the current year, and further 

 careful observations made of the segregations for iiairiness and ray 

 characters. 



It seemed desirable for several reasons to verify the type of coupling 

 or reduplication of the form 2 : 1 :: 1 : 2 described at p. 260. A close 

 study of the various types of coupling may give valuable clues as to 

 the time, mode or place of segregation. The type represented by the 

 above ratio has not hitherto been definitely recognised. Gregory (/. 

 of Genetics, Vol. i, p. 128), however, publishes a result which he suggests 

 may be due to coupling in one sex only, according to the ratio 7:1:1:7. 

 While one must admit the possibility and even the probability of the 

 occurrence of differences of this kind in the sexes, such an interpretation 

 becomes doubtful when we find that the hypothesis of a coupling of the 

 form 2:1:1:2 in each sex explains the result equally well; thus 



Nos. observed by Gregory 



Nos. expected when coupling is of the form 7:1:1:7, and) 

 confined to one sex j 



Nos. expected when coupling is of the form 2:1:1:2, and| 

 occurs in both sexes J 



The results obtained by me this year may be summarized as 

 follows : — 



HR Br hR hr 



Culture 23. Nos. found 128 36 31 18 



Culture 24, „ ... 132 32 25 26 



Both cultures ,, 260 68 56 44 



Expectation, on the basis of coupling of the form) „„„ ^0 cq a a 



2:1:1:2 in both sexes. Eatio:— 22 : 5 : 5 :4i ^^^ ^^ ^^ ^*^ 



Expectation, on the basis of coupling of the form) .-,-5, „„ ^„ .„ 



7:l:l:7inonesex. Katio:-39 : 9 : 9 : 7 | ^^^ ^^ ^^ ^^ 



Further experiments are necessary to determine which of these 

 forms of coupling is actually operative in such cases. In Primula, 

 such experiments would be comparatively easy ; in Senecio, they would 

 be somewhat difficult If the Fi plants are crossed with the recessive 

 parents, thus 



(1) F, ? (HRhr) xP^ (hr) and (2) P ? (hr) x F, ^ (HBhr), 



