Page:American Journal of Sociology Volume 9.djvu/240

 INTRODUCTION TO SOCIOLOGY. V. PART III. GENERAL STRUCTURE OF SOCIETIES.

CHAPTER V. AGGREGATES. Continued.

SEC. IV. DISTRIBUTION OF PLANTS.

ALPHONSE DE CANDOLLE in his analytic botanical geography admirably presents the static and also the dynamic laws of the distribution of plants over the surface of the globe. A rapid glance at the most essential laws relative to vegetable organisms will prepare us naturally for this positive conception of a philoso- phy of the social functions a philosophy which forms the object of this fundamental part of the static at present under discussion.

The distribution of plants from the first is in connection with the several geological epochs. The existing distribution is in connection with the vegetables of former periods. Hence there is a double static correlation of the past with the present. In general, the distribution of vegetable species depends, first, upon the constitution of the different parts of the surface of the globe ; secondly, upon the exposure of the vegetables to the action of the sun and light ; thirdly, upon heat ; fourthly upon humidity.

The plant is a function of the soil and climate. Below o vegetation is arrested, and also beyond a certain degree of heat. The distribution of plants, however, cannot be determined by the average isothermal lines. It depends upon the amount of heat useful for their growth, varying according to the periods of vege- tation, character of soils, etc.

Each species of plants upon the globe, as remarked by Hum- boldt, has its limit, which it is not able to cross ; and Schaw has counted upon the earth more than twenty botanic regions, of which each is the domain of a group of plants altogether dis- tinct, so that, if these groups should become fossils, the geol- ogists would have difficulty in relating them to the same period.

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