Page:Popular Science Monthly Volume 66.djvu/210

206 (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 preceded by crossing. Mutations are probably due to the sudden appearance 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 variation 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 generally only by crossing does variation appear. It is of great advantage to have the parents a certain distance apart in their hereditary tendencies. 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 work 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 lifetime 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 '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 monstrosity than normal individuals are. You are likely to get from sports and monstrosities either extreme of variance. They do not, however, maintain themselves, because heredity pulls back their descendants. A wide variance is more easily pulled back than a slight variance. There are cases where the monstrosity might pull back its species.