238 h^termediates [ch. 



to determine the interrelations of these finer differences. 

 As one of the few points that are clear may be mentioned 

 the impossibility of fixing a form with the sharply-cut 

 division between the white and the colour which is the 

 fanciers ideal for Dutch. From this negative evidence it 

 may be inferred that that particular distribution is not one 

 of those represented as a gametic type. 



Intermediates of this sort are commonly met with in 

 breeding. The "half-dwarf" peas are an instance. In 

 Stocks Miss Saunders has described a *' half-hoary " race 

 (19, p. ^'^ in which the lower surfaces of the leaves were 

 hoary while the upper surfaces were glabrous or nearly 

 so. No such ''intermediates" have occurred among the 

 thousands of plants raised by Miss Saunders except when 

 the definite '' half-hoary " type was originally introduced as 

 a parent. In the Sweet Pea one of the most definite and 

 unchanging types is the nearly white flower with a pink 

 streak, that comes next to the pure white if judged by the 

 criterion of amount of deficiency of colour. In the absence 

 of breeding experiments an ignorant person having raised 

 such a plant as offspring of a purple or a red might consider 

 that he had made an advance towards pure white. Never- 

 theless he would be no more likely to raise true whites from 

 such a tinged white than if he began with a wild Sicilian 

 purple pea. Indeed if I required to raise a white Sweet 

 Pea de novo, I should think the chance of getting it from 

 the wild pea much better than from the tinged white, for 

 again and again wild types have been found to throw off 

 albinos soon after their introduction into cultivation — by the 

 occurrence, of course, of a new genetic variation. 



3. Intermediates pi^oduced by the interference of other 

 factors. There are many intermediates of this kind also. 

 In both animals (Fowl, Rabbit, Mouse) and plants {^Primula') 

 we have seen that a dominant factor may exist which has 

 the power, for example, of suppressing the development of 

 colour, leaving those parts white which in the absence of 

 that factor would otherwise be coloured. This suppressing 

 or inhibiting effect may be total, but when it is not total 

 some puzzling intermediate types may be constituted. Only 

 most careful breeding experiments can reveal the true 



