Bailey.] ^^ [Mayl, 



Domestication. Darwin repeatedly refers the cause or origin of varia- 

 tion to "clianged conditions of life," whicli is essentially the position 

 maintained by the Lamarckians, and he as strenuously combats those who 

 hold that definite variation is an Innate attribute of life. " But we must, 

 I think, conclude . . . ." writes Darwin in the latter book, "that organic 

 beiugs, when subjected during several generations to any change what- 

 ever in their conditions, tend to vary." He discussed, at length, the par- 

 ticular agencies which he considered to be most potent in inducing varia- 

 bility, and enumerated, amongst other factors, the kind and amount of 

 food, climate and crossiog. "Changes of any kind in the conditions of 

 life," he repeats, "even extremely slight changes, often suffice to cause 

 variability. Excess of nutriment is perhaps the most efficient single ex- 

 citing cause." Cope, in his discusfeion of the "Causes of Variation," 

 starts out with the proposition "to cite examples of the direct modifying 

 effect of external influences on the characters of individual animals and 

 plants," and he closes with this paragraph: "I trust that 1 have ad- 

 duced evidence to show that the stimuli of chemical and physical forces, 

 and also molar motion or use and its absence, are abundantly sufficient 

 to produce variaticms of all kinds in organic beings. The variations may 

 be in color, proportions, or details of structure, according to llie condi- 

 tions whicli are present." This is, in great part, the thesis to which 

 Darwin extended the proofs of a most laborious collection of data from 

 gardeners and stock-breeders and from feral nature. It has been the 

 great misfortune of the interpretation of Darwin's writings that his hy- 

 pothesis of natural selection has so completely overtopped everything 

 else in the reader's mind that oilier important matters have been over- 

 looked. 



Whilst the one central truth in the plant creation is the fact that diflfer- 

 ences arise as a result of variations in environment, there are nevertheless 

 many exceptions to it. There are various types of differences which are 

 merely incidental or secondary to the main stem of adaptive ascent. Some 

 of these are such as arise from the cessation of the constructive agencies, 

 and others are mere correlatives or accompaniment of type diM'erences. 

 As an example of the former, we may cite the behavior of tlie potato. 

 By high cultivation and careful breeding, the plant has been developed 

 to produce enormous crops of very large tubers, so heavy a crop that the 

 plant has been obliged to spare some of its energy from the production of 

 pollen and berries for the purpose of maintaining the subterranean pro- 

 duct. It is evident that this high state of amelioration can be maintained 

 only by means of high cultivation. The moment there is a let-down in 

 the factors which have bred and maintained the plant, there is a tendency 

 towards a breaking up and disappearance of the higli bred type. Tiiis is 

 an illustration of the phenomenon of panmixia, as outlined by Weismann, 

 except that the force which has ceased to act is human selection rather 

 than natural selection. "This suspension of the preserving influence of 

 natural selection," Weismann writes, "may be termed Panmixia." In 



