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JOURNAL OF THE ROIAL HORTICULTURAL SOCIETY. 



from two germs both carrying the factor, or 



from two both lacking the factor, or 



from one carrying the factor and one lacking it. 



When the individual is derived from two similar germs, it exhibits 

 and breeds true to the character which those germs carry, whether it 

 is the dominant (here singleness) or the recessive (here doubleness). 



If the individual is derived from one germ which carries, and one 

 which lacks, the factor in question, it exhibits the character represented 

 by that factor (in this case singleness), but it shows its mixed con- 

 stitution in the mixture of the offspring. 



The case of the Wallflower is not quite so simple. In this case 

 the splitting (which here occurs in the petals) may be carried so far 

 as to result in a large number of structures all completely separate. 

 Among the mixed offspring obtained from crossbred singles (singleness 

 being dominant) occur doubles of all grades from the very fully to the 

 very slightly double. The doubles yield only doubles, but to what 

 extent each particular grade breeds true needs further investigation. 



The Welsh Poppy (Meconopsis) affords a converse case to the 

 Wallflower. Singleness is here recessive, and the singles, whatever 

 their parentage, breed true. The doubling, as previously stated, 

 results from petalody of some or all of the stamens, accompanied in 

 the highest grades by petalody of the ovary. The fact that con- 

 siderable grading occurs even among the flowers of one individual 

 introduces a difficulty in classifying these plants and in determining 

 the inheritance of the different grades. 



In the Carnation and Sweet William we probably have two more 

 examples where singleness is recessive to doubleness. 



A particularly interesting case is that of Petunia. Here, according 

 to the evidence up tO' the present, all singles, if self- or inter-bred, 

 yield only singles, but if fertilized with the pollen of doubles, they 

 give a mixed offspring consisting of singles and doubles in the fi.rst 

 generation.'^ Analogy with what we now know to be the case in 

 Stocks (to be described presently) points to the conclusion that here, 

 as in Matthiola, we have the peculiar condition in which the distribu- 

 tion of certain factors is not the same for the male and the female 

 germs of the individual.! 



If we suppose that all the pollen grains of the single carry some 

 factor (or factors) essential to the manifestation of singleness, and 

 that either the ovules of these same singles are mixed and the pollen 

 grains of the double are all alike and all carry doubleness, or con- 

 versely that the pollen of the double is mixed and the ovules of the 

 single all carry doubleness, we can account for the results obtained. The 

 fact that up to the present all the singles crossed with the pollen of 

 doubles have yielded some doubles is in favour of the latter alternative. 



* See " Studies in the Inheritance of Doubleness in Flowers, I. : Petunia," 

 Journ. of Genetics, vol. i. No. 1, 1910. 



t See Re'port IV. to the Evolution Committee, Royal Society, p. 40, 1906, 

 and Journ. of Genetics, vol. i. No. 4, 1911. 



