202 Double Stocks [ch. 



The numerical proportion In which the doubles appear 

 cannot be confidently stated, but It is certain that this pro- 

 portion differs greatly in different strains. There is some 

 reason for supposing the ratio 9 doubles : 7 singles to be 

 the common one in some families, but the experience of 

 breeders points clearly to the fact that the proportion of 

 doubles may be much higher than this in specially good 

 strains, while in others the proportion again may be much 

 lower. Generally speaking, however, we have the certain 

 fact that plenty of strains consist of singles which throw a 

 great excess of doitbles. 



Many writers have recommended special cultural devices 

 for increasing the output of doubles. Starvation, drying the 

 plants off, keeping the seeds from the lower ends of the 

 pods, are among the expedients advised. I do not know 

 that any of these suggestions have been properly tested, 

 and it would be rash to deny that they may have some 

 effect. On the other hand it is practically certain that 

 horticultural bad treatment will not cause a double Stock to 

 produce stamens or carpels. Even in the weakest flowers 

 on the doubles, which often may be so reduced as to have 

 only 4 or 5 petals, no sexual organs are formed. 



The morphological nature of the doubleness of Stocks Is 

 by no means clear. When such flowers are examined it is 

 seen that the 4 sepals are normal. Above them the floral 

 axis Is continued for some length, and on it are set the 

 crowded petals in imbricated fashion. There is no repetition 

 of the sepals as in the case of Arabis albida, and the 

 variation cannot readily be described as a strobilisation. 



Since the doubles are totally sterile, the problem of the 

 hereditary transmission of the condition must be investigated 

 by making crosses with the single-flowered parents which 

 produce these doubles. As the doubleness appears in the 

 offspring* of these singles the condition is evidently present 

 either in the male cells of such flowers or in the female cells, 

 or is produced by the combination (in fertilisation) of the 

 factors with which these cells are endowed. 



Miss Saunders has made many crosses between different 

 strains of double-throwing singles, and as was to be expected, 

 such crosses have given a mixture of doubles and singles 

 just as either parent would have done if self-fertilised. 



