Page:Popular Science Monthly Volume 62.djvu/497

Rh period is passed, and in that case retains its old characters. The new species make their appearance in several, probably in numerous, individuals, and during each year of the mutation period. If they do not do this, their chances of life are exceedingly small, but in the other case their chances are sufficient, even if the new species are not in any regard superior to the mother species. The weaker ones among the new forms disappear of course very early.

The real struggle for life, in which natural selection must decide whether the young types shall continue to exist or not, only comes later on; it is not a war between species, but against other organisms, and against climate and soil.

In 1886, when I was preparing to write my Intracellular Pangenesis, the above mentioned considerations were only partly known to me. De Bary's studies on Draba verna only appeared in 1889, Bateson's book in 1894, Scott's article a little later, etc. But what was known at this time was sufficient to convince me that the formation of species should lend itself to experimental investigation. This was certainly directly opposed to the reigning opinion and especially the conception of a slow and gradual origin was not in favor of my view. It was thought that sudden transitions were limited to the so-called varieties, that they occurred in agriculture and horticulture only, and besides so rarely that an actual study of the problem was not to be thought of.

I then began a more systematic study of the variability of plants, a subject which always had possessed a great attraction for me. It very soon became apparent that observations in nature and in the garden could not lead to the desired goal. Even if one pays constant attention to the same individuals and the same localities, visiting them in various seasons and in different years, the observations remain too incomplete. This is but natural, since mutability commences with the seed and in nature but comparatively little seed, after germinating, attains its full development. I therefore decided to have recourse to sowing-experiments and for this purpose collected as much seed as possible from wild growing plants.

This seed was sown in my experimental garden, in some cases on quite a large scale. Besides I sowed seed gathered from some specimens of wild plants growing isolated in the garden. It was of course my aim to try to find among them one or more species which were passing through a mutation period. Among the seed sown was for instance that of Verbascum thapsiforme, Thrincia hirta, Crepis biennis, Centaurea nigra, Capsella Bursa pastoris, Bidens cernua, Aster Tripolium, Cynoglossum officinale, Sisymbrium Alliaria, Daucus Carota, and a number of other wild plants. As far as possible I allowed myself