150 Inheritance in the Stock (Matthiola incana) 



white-flowered form of incana, from a coastguard station in the Isle 

 of Wight, but I have never again met with it in cultivation nor been 

 able to obtain it through commercial sources except by accident. As 

 I have previously stated^ it is without doubt the unnamed variety 

 described by Linnaeus as " alba nuda vixque tomentusa^." Proved now 

 to be of constant appearance and to breed true it becomes desirable to 

 give it a varietal title, and I propose therefore to name it var. semi- 

 incana. Some account of the relations of this little known form both 

 to the type and to the glabrous variety has already been given ^ but 

 several points still required investigation. With the further evidence 

 now before us we are able to complete the account of the inter-relations 

 of these three forms. Furthermore we gain from the new facts addi- 

 tional insight into the mode of action of the so-called " factors " of 

 Mendelian theory. The trend of the new evidence is strongly towards 

 an interpretation of the factorial scheme, in the present case, in terms 

 of physiological states : towards the conception that a " factor " repre- 

 sents something beyond the mere existence of some definite chemical 

 component — that it stands for something in the nature of a particular 

 condition of physiological equilibrium. A more detailed consideration 

 of this aspect of the subject, however, will be better postponed until we 

 have dealt with the whole body of facts now available. 



From the earlier work it was already apparent that although the 

 half-hoary variety is intermediate in character between the two recog- 

 nised forms on the market, it is not to be obtained by crossing these 

 forms together. It was clear that it must contain some factor which is 

 not present in either, or some combination of factors which is not 

 realised by their union. Matings of semi-incana with the fully hoary 

 type showed full hoariness to be dominant, but a cross with one of the 

 several glabrous (wallflower-leaved) strains led bo the appearance of 

 an entirely new grade — the quarter-hoary, a form intermediate again 

 between the half-hoary and the glabrous condition*. The behaviour of 

 this new form proved that quarter-hoariness was invariably associated 

 with a heterozygous constitution. The quarter-hoary grade cannot be 

 fixed as a true-breeding form as can the fully hoary, the half-hoary and 

 the several glabrous strains, for the quarter-hoary individual produces 

 no gametes of corresponding character. 



^ Journal of Genetics, loc. cit. 



'^ Species Flantaruni, 2nd ed. p. 925, 1762. 



^ Journal of Genetics, loc. cit. 



* Journal of Genetics, loc. cit. p. 152. 



