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I do not see how. Inability to form a clear a priori conception of the process has in itself no validity as an argument against the fact, if fact it be. The progress of biological discovery has repeatedly transformed apparent a priori impossibilities into everyday realities. And if experiment shall really demonstrate the transmission of somatogenic modifications the cytologist has no fundamental obstacle to interpose. The mechanism that his studies have revealed will account for the transmission of all forms of germinal modifications, however they may be caused. The question involved is not of the transmission of the idioplasm or of the germ-cell, but of its interaction with the soma; and this is not an a priori question, but one of fact. Let us admit freely that such an interaction as Darwin assumed may be a real and potent factor in heredity, though it gives no hint of its existence in the visible apparatus of the cell. In the present defective state of our knowledge we may well grant that there may be many a thing between germ-cell and body that is not yet dreamed of in our biological philosophy. But has the transmission of acquired characters, in the strict and proper sense of that much abused phrase, been demonstrated? If in closing I venture to question this, I pray that my sins be not visited upon the study of the cells, but upon a failure to discover the demonstration in other fields of inquiry.

THE DIRECT INFLUENCE OF

ENVIRONMENT

BY

D. T. MACDOUGAL

ANY serious consideration of the diversity of organisms, of the complexity of the qualities they bear, of the relationships they sustain, and of the character of the stresses under which they exist with relation to the environmental setting, leads inevitably to the conclusion that their evolutionary development must have been affected by many modifying agencies; that the origination, or activation of their qualities or characters may not be ascribed to any single causal force or guiding factor; and that the course of heredity from generation to generation has been determined by many things beside the simple inertia of primitive initial qualities of protoplasm.

When we join in the accepted generalization that the qualities and forms of organisms now existent are the net result of the action of environic forces upon ancestral structures, selective as well as initiatory, we implicate a much larger group of conceptions than that embodied in the present thesis, since it is the intention to confine discussion to the possibilities that arise when liv

ing or self-generating matter transmits its specialized characters from one generation to another in the germ-cell, and displays its periodic somatic expansions in ontogeny.

Within this definite and restricted field, exactness and clearness of comprehension of the relations involved will depend directly upon the thoroughness with which we may be able to connect our conceptions with the physico-chemical processes of organisms.

The more important external, direct, or physical factors, the influence of which induces adjustments and engages the activities of protoplasm, include radiant energy in its various phases, and the chemical structure of the medium, substratum or substances coming into contact with the living matter and included with its intake and output. These agents interlock intimately with the parts of the self-generating protoplasmic machine, furnishing building material, energy in various forms, catalysts, and control reactions in a manner so intimate that it is impossible to think of living matter free from its environic setting.

Now if we set about the calibration of the quantitative relation of any of these factors to living matter, or attempt an estimation of the qualitative effect, we will find that, with respect to any given strain of organisms or any individual, the constellation of specific activities, processes or functions, grouped in the plant are adjusted in such manner that they proceed at the most advan

tageous rate with relation to each other within, for example, some narrow range of temperature. In our easy acceptance of the obvious, we are apt to assume that these optimal conditions are furnished by the native habitats of plants, or in other words, the place they happen to occupy in their movements about the world when they are called to our attention. Now, on the one hand, plants simply are found in areas they have been able to reach, and "native habitats " may by no means offer the optimal conditions, a condition of affairs of which more than a hint is furnished by the irruption of weeds, followed by a development of a vigor unknown within the previous range of the species. On the other, the reminder is necessary that no one habitat may furnish the optima for the accomplishment of all of the processes involved in the ontogeny and reproduction of the individual, and all environic relations include groups of compromises and of adjustments that put the capacity of the living matter to the utmost stresses it may bear.

Two main considerations arise when attention is directed to the behavior of the organism as it encounters the external factors in unusual intensities, an experience which has been countlessly repeated and which is one of the eliminating factors in selection. The first concerns the mechanism of the adjustment of the individual to altering environment, and the second, the possibilities of transmission of the effects of the adjustment

to the progeny, both in functional capacity and accompanying structure.

ADJUSTMENT OF THE INDIVIDUAL TO ALTERING ENVIRONMENTS

Let us take, for example, a plant standing in the open in a habitat in which it is firmly established, and introduce some modifications of wide range of the insolation, which may or may not register with anything previously encountered by this individual. The primary or direct effect of the change will undoubtedly be a modification of the reaction-velocities of some of the chemical processes so that metabolism and all of the lifephenomena dependent upon it will undergo alterations in rate, cell-division, chromosomatic involution, catalyptic action involving respiration, intake and excretion, and finally growth also. A secondary effect accompanying these changes will be due to the irritability of the living matter by which sudden changes in almost any external factor will exercise a releasing or unloosing action. Outward manifestations of such action are seen in the various thermotropic and heliotropic movement of leaves, and while there seems to be a disposition on the part of some physiologists to eliminate metabolic activities from the realm of irritable reactions, yet it does not seem justifiable upon present evidence.

Whether an irritational phase intervenes or not, when an environmental factor undergoes

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