478 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



or by crossing, must reveal. That such is in fact the case I think 

 we may now regard as fully established. The case is, moreover, one 

 of special interest, for we have to deal here with a character which 

 cannot be transmitted by those individuals which exhibit it, for such 

 individuals are completely sterile. No double can leave posterity, 

 and yet some strains produce more doubles than singles in every 

 generation. The singles of these strains are indistinguishable to the 

 eye from other singles which have not this power, and these double- 

 throwing singles, moreover, produce the doubles in definite ascertain- 

 able proportions which are constant for individuals of the same consti- 

 tution. These various facts we are now in a position to explain. 



If we start with an individual or a strain of Stocks which is 

 found to give exclusively single offspring, we may now confidently 

 expect that all successive generations derived from these offspring 

 will consist entirely of singles, provided that the plants are allowed 

 only either to interbreed among themselves or to be qrossed with other 

 strains which similarly yield offspring all single. And this result 

 follows whether the plants are supplied with much water or with 

 little, whether they are grown in a rich soil or a poor one. We can 

 account for this uniform result in each successive generation of the 

 descendants on the supposition that the individual with which we 

 started contained certain factors, the presence of which causes the 

 flowers to be single; and further that these factors causing singleness 

 were brought in from both sides of the pedigree — that is to say, that 

 they were borne by both the contributing germ cells (by the egg cell in 

 the ovule and by the male element in the pollen tube), so that the 

 resulting individual was homozygous in respect of these factors. An 

 individual will contain the factors in respect of which it is homozygous 

 in all its germ cells; consequently an individual thus constituted in 

 regard to the factors for singleness will produce offspring all single, 

 and these offspring will in turn produce successive generations, of 

 singles. 



The singles of the other class — of the double-throwing strains — 

 also give constant and uniform results. If we take an individual 

 belonging to one of these strains and self-fertilize it we obtain a mixed 

 offspring of singles and doubles, the doubles being in excess. If these 

 single offspring are again self-fertilized or inter-bred they again yield 

 a mixture in the same proportions as before, and this result obtains 

 in all the succeeding generations. The individuals of these strains, 

 with, so far as we know, but one exception (see p. 481), breed true 

 in respect of all other characters which have been investigated, such as 

 colour of the cell-sap in the petals — whether various shades of red 

 or purple, or colourless; colour of the plastid bodies — whether cream 

 or uncoloured; colour of seed — whether of some shade of brown or 

 green; character of the leaf and stem surface — whether fully hoary, 

 half hoary, or destitute of hairs as in the wall-flower-leaved forms : but 

 in regard to singleness they are constitutionally incapable of breeding 

 true; they have the habit known as "ever-sporting." The explana- 



