Page:Popular Science Monthly Volume 69.djvu/211

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207
VARIATION IN PEDIGREE-CULTURES
DISCONTINUOUS VARIATION IN PEDIGREE-CULTURES[1]
By Dr. D. T. MACDOUGAL
DIRECTOR, DEPARTMENT OF BOTANICAL RESEARCH, CARNEGIE INSTITUTION OF WASHINGTON

HEREDITY may be defined as that appurtenant function of living matter by which qualities, characters and capacities are transmitted through successive generations. The absolute identity, or measurable expression, of the inherited characters may be qualified by partial and individual fluctuations about a norm in a continuous series in the progenies, and these characters, singly or in groups, may be subject to dominations, recessions, integrations and resolutions in hybridizations, or to various forms of combination, actual or apparent. In the case of discontinuous variations or mutation, single or unit characters, or constellations of them, may be activated, or converted into a latent or perlatent condition.

 

Methods of Investigation

Owing to the stimulus of recent discovery, attention is focused at the present time upon the ultimate result of fluctuating variability as influenced by various agents, in the origin and fate of hereditary strains, species, races or physiologically unified groups of organisms, and upon the probable part played in the matter by the saltatory movements, which are being brought to notice so plentifully in all quarters. In connection with the last-named feature, the behavior of the individual qualities or unit-characters in hybridizations are being studied with enormous zeal as offering a ready analysis of the action of inheritance. The comparative ease with which hybrid combinations of plants are effected, and the simplicity of the subsequent resolutions in the progeny, render this phase of the subject easy of attack, and results are being obtained, which, if one may judge from recent literature, do not seem available to many writers.

It needs but a moment's consideration to bring the realization that the entire subject offers some of the most abstruse and difficult problems in the whole realm of biological science. Intricate and elusive in their physiological complexity, we may hope to uncover the main factors by perfected methods in research upon the ultimate mechanical basis of heredity coupled with a refinement of technique in dealing with the course of inheritance as we trace it from generation to

  1. Lecture given at Marine Biological Laboratory, Woods Holl, July 20, 1906.