Page:Popular Science Monthly Volume 69.djvu/225

Rh discontinuous variations or mutations are essentially vegetative, yet these are generally termed so exclusively. It is to be noted that such sports, or mutants, when closely fertilized, come true to their aberrant characters. Among other numerous conclusions sustaining this point, one which has recently come to notice again is that of Kerner, who said:

The fact is that all plants may at some time sooner or later produce an aberrant branch, which differs from the parental type in many characters, and numerous phenomena force us to the conclusion that under the conjunction of favorable circumstances such aberrants would become the starting points of new species.

In the context the author is careful to point out the limitations of such a method of origin of forms.

Actual pedigrees from such sports or aberrant branches have been tested, in one instance by de Vries and in two others by myself, with the unanimous result that they were found to be constant to their aberrant characters.

Having carried on such pedigree-cultures with a large number of species for several years and having encountered some which did and others which did not give rise to aberrant individuals, attention was directed to the possibility of inducing changes in the hereditary elements in such a manner that the qualities transmitted would be altered or destroyed. A theoretical consideration of the subject seemed to indicate that the changes constituting the essential operation of mutation ensued in a stage previous to the reduction divisions in the embryo sac, or the pollen mother cells. It was planned therefore to subject