128 Experiments with Primula sinensis 



terms. On the basis of the 3:1:1:3 system of partial coupling, the 

 122 plants of which the family consists should be distributed in tlie 

 proportions of 



78'1 magenta, green stigma : 133 magenta, red stigma : 



13'3 red, green stigma : 17 '2 red, red stigma. 



The distribution thus calculated would, however, give magenta : red = 

 green stigma : red stigma = 3:1, while the observed numbers are 

 magenta 85, red 37 ; green stigma 88, red stigma 34. That is to say, 

 tliere is a deficiency of plants bearing the dominant characters, and, 

 consequently, the first term will be smaller and the fourth term will 

 be larger than the calculated numbers. Apart from this divergence, 

 there is a close approximation between the observed and calculated 

 numbers, and there can be little doubt that the partial coupling was 

 of the type 3:1:1:3. 



The crosses between " Orange King " and " Snowdrift " have given 

 results which may perhaps allow of the same explanation, but in the 

 remaining experiments the fourth term is definitely smaller than the 

 middle ones. Each family was raised from seed obtained from several 

 capsules borne on one plant ; and, until the completion of experiments 

 which are now in progress, it is not possible fully to analyse the 

 results. For the time being it may be pointed out that a very close 

 approximation to the observed numbers is given by the assumption 

 that a coupling of the form 7:1:1:7 is present in gametes of one 

 sex only, gametes of the opposite sex being pi-oduced in equal numbers 

 of all four kinds. The numbers are 



Observed 



Calculated for 7:1:1:7 coupling 

 in gametes of one se.v only 



As was stated above^ the distribution of the four kinds of offspring 

 in the i^„'s from the cross ("Crimson King" x "Snowdrift") gives no 

 clear indication of the existence of any form of partial coupling during 

 gametogenesis of the F,. In two Fo families raised in 1907, the results 

 differ very little from the simple 9:3:3:1 ratio. In the later experi- 

 ments there is some departure from this ratio, principally due to the 

 dearth of plants carrying the positive characters, magenta and green 

 stigma. 



' p. 113. 



