[BN] Origin of Species, 6th. ed. chap. iv. p. 100.
[BO] Contributions to the Natural History of the United States, Introduction, Boston, 1857; and Essay on Classification, p. 15, published separately; London, 1859. See [Appendix VI.]
[BP] Origin, 4th ed. p. 143.
[BQ] Origin of Species, 6th. ed. chap. iv. p. 100.
LECTURE V.
RELATIONS OF LOWER AND HIGHER ORGANISMS.
From the general aspects of the theory of species, we pass to the consideration of distinct groups of organism, with the view of ascertaining their relations to each other. In doing so, it is better to begin at the lower end of the scale, leaving for a more advanced stage of inquiry the higher types of organism. In this department of the subject, special obligations are due to the wide range of investigations either occasioned or stimulated by the theory of evolution. For, whatever may be the ultimate award passed on this theory, there will be a unanimous recognition of the great value to science attending on the varied forms of inquiry stimulated by the writings of Mr. Charles Darwin. And one obvious and strong reason for such acknowledgment is that so many of the results of these researches have an inherent value quite distinct from their testimony in favor of the theory that the struggle for existence is the principal factor in the origin of new species.
One of the most interesting fields of observation thus opened, is that concerned with the fertilization of plants by the intervention of insects and birds. A beginning in this department was made by the German naturalist, Christian Konrad Sprengel, who published in 1793 the report of his observations. In this he has been followed by Darwin, in 1862; by Dr. Hooker, Professor Asa Gray whose contributions appeared in the American Journal of Science and Art in 1862, and 1863, Moggridge, Fritz Müller, and Sir John Lubbock. The facts now accumulated, rank as an important contribution to botany and zoölogy, and naturally fall within the circle of recent advances to which it is desirable that attention be turned.
The general result is one of great interest, as illustrating a striking degree of interdependence between lower and higher organisms,—the vegetable and animal kingdom contributing to each other's subsistence and propagation. Flowers present special attractions to insects flying around, alluring them by varied colors, and providing for them by secreting stores of honey; on the other hand, these insects (flies, bees, wasps, etc.), seeking the honey which satisfies their wants, at the same time carry the pollen from one flower to another, thus providing for the fertilizing of the plants. In some cases, fertilization is secured by a natural process within the organism itself; in other cases, the pollen is scattered over a region by the wind; but the most wonderful, and at the same time efficient mode of providing for the growth of vigorous plants, is fertilization by the agency of insect life.
A brief outline of the ordinary structure of the flower will introduce to a ready appreciation of the scientific interest attaching to this last mode of fertilization, both as concerning the functions of different portions of the flowers, and the relation of dependence established between higher and lower forms of organism, so that each is dependent on the other.