108 FACTORS OF EVOLUTION 



which they wish to paint, and inoculate the fresh wound with 

 the milky secretion from the skin of a small toad. The feathers 

 grow of a brilliant yellow colour, and on being plucked out, it 

 is said, grow again of the same colour without any fresh opera- 

 tion." Although this change seems to be producible at will by 

 a definite agent, we really know no moi-e concerning the actual 

 steps of the process by which it is produced, than we know con- 

 cerning the intimate nature of the changes by which the peach- 

 branch is metamorphosed into a nectarine-branch. The possibility 

 of the occurrence of the molecular change which occasions this 

 metamorphosis is, moreover, by no means limited to the buds of 

 the peach-tree. For, as Darwin tells us, " nectarines have likewise 

 been produced from the stone of the peach, and, reversely, 

 peaches from the stone of the nectarine." And even this is not 

 all, since " the same flower-bud has yielded a fruit one half or 

 one quarter a nectarine, and the other half or three quarters 

 a peach." 



So much then for facts concerning 'sports' and 'discontinuous 

 variation ' which have been known for rather a long time. Let us 

 look now to the more recent evidence tending further to show in 

 an unmistakable manner that even in regard to higher forms of life 

 the origin of new species may occur by sudden ' mutations ' rather 

 than by the slow cumulation through many generations of minute 

 progressive variations. 



In his recent important work Prof, de Vries seems to have cer- 

 tainly demonstrated this point in regard to the 'Evening Primrose' 

 {CEnothera Lamarckiana) by means of observations carried on 

 during ten years upon 50,000 of the descendants of some of these 

 plants placed by him in the botanical gardens of Amsterdam. 

 Preliminary experiments made with this and a number of other 

 plants showed it to be favourable for such observations. Of the 

 50,000 descendants of this plant, it was found that " about 49,200 

 were in no respect different from the original patriarchal 0. 

 Lamarckiana, showing no tendency towards gradual change in any 

 special direction, but only the common small fluctuating ' variations ' 

 as regards size and appearance on either side of a normal — in 

 fact, resembling in that respect other plants and animals which are 

 left to themselves without being interfered with." 



" Quite otherwise with the 800 other plants. None of these, 

 although appearing spontaneously, could be said to be representa- 



