STAGES OF VITAL MOTION. 21 



Effects of Inbreeding. 



These stages or states of evolution are distinguished and named in 

 the belief that they will afford a useful addition to our evolutionary 

 vocabulary. They are, however, parts of a connected series of events 

 with no lines of separation between them. All organisms which too 

 close segregation has brought to the catalytic stage have passed through 

 the hemilytic. For example, the recently domesticated pecan tree of 

 our southwestern states is still in the first or normal stage of evolution, 

 and only a small proportion of the seedlings produce nuts like those 

 of the parent tree. Selective inbreeding for a few generations would 

 first produce imiformity, or 'fix the type,' as the expression is, by in- 

 ducing the hemilytic or retarded stage of evolution, while a too narrow 

 and persistent selection or the segregation of a single line of descent 

 would hasten the decline and eventual destruction of the very type it 

 might be designed to perpetuate. Coffee has not been domesticated for 

 much more than a thousand years, and although selection has not been 

 practised, very pronounced and constant variations are now appearing 

 in considerable numbers, but all less fertile than the parent stock. 

 That inbreeding tends to 'fixity' of characters is true only for a time; 

 organisms in the catalytic stage are rendered less uniform as well as 

 less fertile by continued inbreeding. Uniformity and vigor can be 

 restored, as breeders already know, only by the repetition of the pro- 

 cess of selective segregation after cross-breeding with another stock. 



The catalytic stage is attained more slowly by asexual propagation, 

 and the variability is far less pronounced, but partial or complete ste- 

 rility has appeared in a considerable series of unrelated tropical plants 

 long propagated only by cuttings, such as the banana, pine-apple, sugar- 

 cane, sweet-potato, Irish potato, taro and yam. 



Parthenogenesis may also be viewed as a form of asexual propaga- 

 tion, and habitual self-fertilization is another stage of sexual and evo- 

 lutionary decline. Self-fertilization is supposed to be normal in sev- 

 eral of the cereal grasses and in many other plants, though it is obvi- 

 ously unsafe to infer that cross-fertilization is entirely superfluous 

 because frequently absent. With the cereals and other plants of sim- 

 ilar history self-fertilization may prove to be a result of cultivation in 

 northern latitudes where the weather is often unfavorable for pollina- 

 tion by the wind or by insects, so that selection would encourage varia- 

 tions least dependent upon cross-pollination. I learn from Mr. Jesse 

 B. Norton that the more primitive, hardy, and disease-resistant oat 

 varieties of South Europe open their glumes widely and thus invite 

 cross-fertilization, while in most of the varieties bred in the colder and 

 more rainy climate of Northern Europe the glumes separate much less, 

 and do not expose the stigmas, thus showing that cross-fertilization has 

 been abandoned. Darwin proved that there is no benefit in the cross- 



