252 Inheritance in the Groundsel 



These experiments indicate that cream is recessive to yellow ; the 

 seven rogues in Exp. 33 must have been heterozygous for yellow and 

 cream, and due to an accidental cross with a yellow RR form. 



Seeds were also saved from several of the yellow types of the F^ 

 generation, and as it sometimes proved advisable (colour was not the 

 sole problem under investigation) to select other parents than those 

 originally selfed, the results must be read with the necessary caution. 



1909. ^2. No. 2. YeUow, selfed. 



1910. F3. Exp. 35. 108 plants. 



1 



r- 1 



85 yellows 23 creams ; of these Nos. 9 and 37 were selfed. 



No. 9. No. 87. Slight yeUow tinge in cream, 



I I and tested for that reason. 



1911. ^4. Exps. 36 and 37. 49 plants, cream. 49 plants, cream. 



This result proves the dominance of yellow. No. 2 was clearly a 

 heterozygote. 



Two other yellows, Nos. 243 and 297, were tested and proved to be 

 homozygotes. The record for one is given below ; that for the other is 

 similar. 



1909. F2. No. 297, yellow, not selfed. 



1910. F^ . Exp, 39. 36 plants, of which 3 were NR and were destroyed. 



3 Deducting these, there were left 



33 plants, all yellow, of which No. 34 was selfed. 



No. 34. 



I 

 1911 F4. Exp. 40. 49 plants, all yellow. 



We can now accept the following notation, GG, Gc, cc, for the three 

 types found, cc signifies creams ; GG yellows. 



The progeny of a sixth plant, however, was the means of elucidating 

 the cause of the rarity and variability of the creams in the F^ generation. 

 If there is a factor X dominant over another x and cream colour can 

 only appear in the plant when cc is associated with xa;, being wholly 

 suppressed by XX and almost wholly by Xx, then it is clear that in 

 a generation where these two pairs of factors are segregating normally, 

 there will be one-fourth of the individuals of the type xx and one-fourth 

 only of these xx individuals also of the type cc, and therefore one- 



