Page:Popular Science Monthly Volume 69.djvu/229

Rh test and observation, a matter which may occupy some time, before final announcement.

Despite general assertions to the contrary, no evidence has yet been obtained to prove that the influence of tillage, 'cultivation,' or the mere pressure of environmental factors has produced any permanent changes in hereditary characters of unified strains of plants.

The above is not meant as a sweeping assertion that inherited characters may not be affected by agents external to the protoplasts that bear them. On the contrary, the experiments now well advanced and conclusively verified, first announced in December, 1905, and here described for the first time, show that saltatory inheritance has been induced by the action of external agents upon the ovules of two species of seed-plants. The alterations in question consist in the total suppression of some qualities of the parental form and the substitution therefor of new characters or of a total gain of new qualities in some instances, and the differentiating points between the parental form and the derivative are both anatomical and physiological.

The atypic form which has been tested to the second generation in one species is found to constitute a mutant in the sense in which that term is used by de Vries, and is a real and actual departure from the course of the hereditary strain. The capacity of the mutants induced in this manner for survival would depend entirely upon the environment into which they might be thrown.

If we seek a similar possible intervention of external forces which might act upon the plant unaided by man, we might find such influence coming from radio-active substances, such as spring-and rain-water, or from the effects of sulphurous and other gases which are being set free in numberless localities, or the protoplasts most nearly in contact with the egg-apparatus may well excrete substances which would produce the same effect, without regard to the forces which originally caused the disturbances in the extra-ovular tissue. Lastly it is to be said that the actual technique of injection might be imitated in a measure by the action of foreign pollen which might find lodgment on the stigmatic surfaces, and sending down tubes through the style introduce unusual substances to the vicinity of the egg-cell without participating in normal fertilization, which would ensue in the customary manner. Lastly it is to be said that it would appear that a most prolific source of such disturbances might be expected to result from the stings and lacerations of insects, or the action of parasitic fungi, both sources of the most profound morphogenic alterations in somatic tissues, profusely exemplified by the well-known gall formations of plants.