Page:The Scientific Monthly vol. 3.djvu/319

 THE SCIENTIFIC MOISTTHLY

��OCTOBER, 1916

��THE ORIGIN AND EVOLUTION OF LIFE UPON THE

EARTH, III*

Bt henry FAIRFIELD OSBORN

COLUUBIA UNIYBBSITTj AMEBICAN MUSEUM OF NATURAL HI8T0BT

LECTURE I. PART IV

Contrasts between Plant and Animal Evolution — ^Mutation of de Vries in Plants — Resemblances between Plant and Animal Evolution — Origin of Animals — ^liife of Lower and Middle Cambrian Times — Adaptive Radiation of the In- yertebrata — ^Mutation of Waagen in Molluscs.

Contrasts between Plant and Animal Evolution

In their evolution, while there is a continuous specialization and differentiation of the modes of obtaining energy, plants do not attain a higher chemical stage than that observed among the bacteria and algae, except in the parasitic forms which feed both upon the plant and animal compounds. In the energy which they derive from the soil plants continue to be closely dependent upon bacteria, because they derive their nitrogen from nitrates generated by bacteria and absorbed along with water by the roots. In their relations to the atmosphere and to sunlight the chlorophyllic organs differentiate into the marvelous variety of leaf forms, and these in turn are separated upon stems and branches which finally lead into the creation of woody tissues and the clothing of the earth with forests. Through the specialization of leaves in connection with the germ cells flowers are developed, and plants establish a marvelous series of life environment interactions, first, with the developing insect life, and finally with the developing bird life.

The main lines of the ascent and classification of plants are traced by paleobotanists partly from their structural evolution, which is

1 Fourth course of lectures on the William Ellerj Hale Foundation, Na- tional Academy of Sciences, delivered at the meeting of the academy at Wash- ington, on April 17 and 19, 1916. The author desires to express his special acknowledgments to Dr. M. A. Howe, of the New York Botanical Garden; Pro- fessor Charles Schuchert, of Yale University; Professor Gary N. Calkins, of Columbia University and Mr. Roy W. Miner, of the American Museum of Natural History, for notes and suggestions used in the preparation of this section.

VOL. III. — 2?.

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