VARIATION 445 



percentage of them ; and Darwin mentions a famous weeping 

 oak at Moccas Court which transmitted its special character to 

 all its seedlings, though in varying degrees. 



According to our theory, the transmission of a variation by 

 seeds depends on the presence of a corresponding moditication 

 in the majority of the determinants in the germ-plasm of the 

 seeds. If the germ-plasm contains a hundred ids, the con- 

 trolling forces of which are equal, more than fifty determinants 

 N must be transformed into N^ before the modification would 

 be perceptible in the seedling. Since therefore, as was re- 

 marked above, new variations probably never appear simultane- 

 ously in all the determinants, but only in a varying percentage 

 of the ids, the chances are greatly against all the seedlings 

 produced by the transformed plant exhibiting this modification. 

 For every germ-cell has undergone a ' reducing division,' and 

 hence many of them will always only possess a minority of the 

 modified determinants N^, and this may even be a very small 

 one if the majority i/i the germ-plasm of the parent-plant was 

 small. When two Aich cells unite in the process of amphimixis, 

 the resulting germ-plasm contains only a small minority of 

 modified determinants N\ and the modification is inappreciable. 

 This accounts for the fact that the seedlings of a variety hardly 

 ever reproduce the variety in all cases ; and that in rarer in- 

 stances, such as that of the weeping oak already mentioned, 

 all the seedlings may exhibit the corresponding variation, al- 

 though in varying degrees. For the composition of the germ- 

 plasm must differ in each of them in consequence of the 

 processes of ' reducing division ' and amphimixis, even when the 

 parent-plant contains only a small but ever varying minority of 

 ancestral determinants. 



We can, moreover, easily account for the fact that seedlings 

 of a variety, such as the balsamine, may resemble the parent- 

 plant, without transmitting the character of the variety to their 

 offspring. In this case all the daughter-plants of the variety 

 in question must retain a majority of the modified determinants, 

 but in very varying degrees. In those which contain a very 

 large majority in their germ-plasm, it necessarily follows that the 

 larger number of the germ-cells produced must contain a major- 

 ity of modified determinants ; but in the case of those in which 

 the proportions are more equal, the chances are in favour of the 

 seedlings containing only minorities of these determinants. 



