GERMINAL SELECTION 141 



germ-plasm, which gave rise to variations in certain determinants. 

 There was still lacking the recognition that the direction of variation 

 once taken must be adhered to until resistance was met with, and 

 that the determinants stand in nutritive correlation with one another, 

 so that changes in one determinant must re-act upon the neighbourin<»- 

 ones, as I shall explain more fully afterwards. I also showed from 

 definite cases that such sports, though they, are sudden — ' saltatory ' — 

 in their mode of occurrence, are long being prepared for by intimate 

 processes in the germ-plasm. This ' invisible prelude ' of variation 

 depends on germinal selection. When a wild plant is sown in garden- 

 ground it does not require to vary at once; several, even many, 

 generations may succeed each other which show no sports ; suddenly, 

 however, sports appear, at first singly, then, perhaps, in considerable 

 numbers. It is not, however, by any means always the case that 

 considerable numbers occur, for some varieties of our garden flowers 

 have arisen only once, and then have been propagated by seed ; and 

 such saltatory sports in plants which are raised from seed are usually 

 constant in their seed, and if they are fertilized with their own pollen 

 they breed true — a proof that the same variations must have taken 

 place in the relevant determinants in a large majority of ids. 



In animals, it would appear, such saltatory variations occur 

 much more rarely than in plants ; the case examined in detail by 

 Darwin of the ' black-shouldered peacock ' which suddenly appeared 

 in a poultry-yard is an example of this kind. Much more numerous, 

 however, are the instances among plants, and especially among plants 

 which are under cultivation. This indicates that we have here to do 

 with the effect of external conditions, of nutritive influences which 

 cause the slow variation of certain determinants, sometimes abetting 

 and sometimes checking. As soon as a majority of ids varied in this 

 way comes to lie in a seed, a sport springs up suddenly and apparently 

 discontinuously — a plant with differently coloured or shaped petals 

 or leaves, with double flowers, with degenerate stamens, or with some 

 other distinguishing mark, and these new characters persist if the 

 variety is propagated without inter-crossing. 



But it happens sometimes, though more rarely, that not the whole 

 plant but individual shoots may exhibit the variation. To tliis class 

 belong the ' bud- variations ' of our forest trees, the copper-beeches, 

 copper-oaks, and copper-hazels, the various fasciated varieties of 

 oak, beech, maple, and birch, and the 'weeping trees'; also the 

 numerous varieties of potato, plantain, and sugar-cane. It seems that 

 only a few of these breed true when reproduced from seed, or in other 

 words, they usually exhibit reversions to the ancestral form : on the 



