2o6 POPULAR SCIENCE MONTHLY. 



(perhaps oftener), also, by starvation; new variations oftenest by rich 

 soil and general prosperity. There is no evidence of any limit in the 

 production of variation through artificial selection, especially if pre- 

 ceded by crossing. Mutations are probably due to the sudden appear- 

 ance of latent tendencies in new combinations, producing novel effects 

 analogous to new chemical combinations." 



" Mutation is not a period, but a state induced by various hereditary 

 and external conditions. It is not by any means certain that there 

 is any period in the life-history of the species when it is more subject 

 to mutation than at other times, other conditions being similar. By 

 crossing different species we can form more variations and mutations 

 in half-a-dozen generations than will be developed by ordinary varia- 

 tion in a hundred or even a thousand generations." 



" The La France and some other roses, as well as dahlias, callas and 

 many other plants, every once in a while throw out, on some particular 

 year, a number of unusual sports in various localities. This is probably 

 a matter of season, the forces outside bringing about parallel mutations. 

 The evolution of species is largely dependent on crossing the variations 

 contained within it. Forms too closely bred soon run out, because gen- 

 erally only by crossing does variation appear. It is of great advantage 

 to have the parents a certain distance apart in their hereditary tenden- 

 cies. If too close together there is not range enough of variety. If 

 too far apart, the developed forms are unfitted for existence because 

 too unstable. Correlated changes ivork together to produce the effect 

 of mutations. Environment effects a permanent change in species by 

 selection of those which fit it or by producing changes in individuals 

 which are better equipped to survive. Heredity is the sum of all past 

 environment, conditions both latent and apparent. Latent traits often 

 arise when circumstances make them possible. Environment of a life- 

 time does not necessarily or usually appear in another lifetime, but 

 continues in the same direction and will strike into the nature of the 

 plant in time. We may refer to Emerson's remark on the ' baking into 

 the picture of the pigment laid down by environment.' Selection is 

 1 cumulative environment.' Fortuitous variations occur everywhere. 

 They come up all the time, from past environments, past heredity and 

 present opportunity. No two individuals are alike. Where there is a 

 marked tendency in one direction, we have the case of a persistent effect 

 of environment. Monstrosities are engorgements of force. They are 

 generally a thousand times more likely to. develop another sort of mon- 

 strosity than normal individuals are. You are likely to get from 

 sports and monstrosities either extreme of variance. They do not, how- 

 ever, maintain themselves, because heredity pulls back their descend- 

 ants. A wide variance is more easily pulled back than a slight variance. 

 There are cases where the monstrosity might pull back its species. 



