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The prompt mention in our list of "Books of the Week" will be considered by us an equivalent to their publishers for all volumes received. The interests of our readers will guide us in the selection of works for further notices.

DARWIN'S BOTANICAL STUDIES.*

BY PROFESSOR ASA GRAY, LL D.

THREE of Mr. Darwin's volumes relate to the economy of flowers as regards reproduction, and to the adaptations of many of them to be benefited by the visits of insects. These volumes; taken in the order of publication, are: 1. That on "The Various Contrivances by which Orchids are Fertilized by Insects," brought out in 1862, but re-elaborated recently in a second edition, which appeared early in the past year; 2. "The effects of Cross and Self-Fertilization in the Vegetable Kingdom," which was published in the year preceding;3. The volume now before us, which concludes the series, but which is in part of much earlier date; about half the volume being a reprint, with many additions and some corrections, of two or three papers which were contributed to the Linnæan Society of London and published in its journal, one of them in the same year in which the book on orchid fertilization first appeared. These papers were hardly accessible to general readers, and yet are necessary to the full presentation of a very popular and fascinating subject, which Mr. Darwin has made his own. Not that this volume—or either of the three—is light, popular reading; for this, in particular, is filled with statistics and tables and numerical details, and the topic is too remotely associated with what is called Darwinism to derive an adventitious interest from the "Origin of Species " and the "Descent of Man." But it has an interest and a value of its own—one which is shared by two preceding works of Mr. Darwin, which should be reckoned in the series—that on climbing and that on insectivorous plants.

While Darwin's other and more famous works have opened new channels of thought and new lines of speculation, these have led into new fields of observation and of easy research —not in far-off regions, or under the microscope, which comparatively few can possess or be trained to use; but in the common things which are everywhere around us, in which, with newly-opened eyes, we may now read new meanings, and discern plans, adaptations, contrivances which the philosophers of the past generation never dreamed of, but which are made so plain that even a child may mainly understand and be interested in them. The educational value of this new knowledge can hardly be overestimated and is only beginning to be felt.

Our meaning may be illustrated from the matter which first presents itself in this book on The Different Forms of Flowers on Plants of the Same Species. Why should a plant have two kinds of flowers? When the two kinds are of opposite sexes—as in willow trees—the immediate reason why is obvious enough. But in the cases which first take our author's attention both kinds are equally perfect, both have stamens and pistils, and, therefore, all that is requisite for seed-bearing. Why should individuals raised from seeds of the same pod differ in their flowers, and yet all the flowers be perfect? The difference is one which a casual observer would not be likely to notice. Not many of those who adorn their rooms with pots of Chinese primroses in winter, or of English primroses in spring, or who gather Houstonias in our low meadows, have observed that, while in the blossoms of one clump the tip of the pistil projects, in those of another clump the same position is occupied by the tips of the anthers; that when the tip of the pistil, or stigma, is exposed at the orifice of the flower the stamens are situated lower down within; that when the anthers project the shorter pistil places the stigma of that flower at the same hight as the anthers of the other. Still, this reciprocal relation has long been known to botanists, and in the case of primroses the English florists have names to designate the

*The Different Forms of Flowers of Plants of the Same Species. By Charles Darwin, LL D. London; Murray. New York: D. Appleton & Co., 1877. Pp. 352.

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two sorts. Mr. Darwin has the credit not of discovering the two kinds, but of finding out the meaning of it.

In the first place, he saw that here was something to be explained. He was not content, as his predecessors were, with noting that the thing was so; but he assumed that there was a reason why. And he then set to work, in the true inductive mode (but not in Lord Bacon's way), to discover this reason. He conceived an hypothesis of a general principle which would completely explain these cases. He found that it would equally explain a great variety of other cases; that within its proper limits it would explain them all; and he, therefore, inferred that the supposed principle was a true one. The principle is that "Nature abhors perpetual self-fertilization"; or, expressed without metaphor and in its application to the case in hand, that these flowers, though consisting of both sexes and capable of self-fertilization, were intended to act as if of separate sexes—that the pollen from the anther of one kind of flower was intended to reach and fertilize the pistil of the other kind, and so reciprocally. He then confirmed this particular supposition by observation; saw that certain insects, habitually visiting these blossoms for nectar or other food, actually carried pollen from the high anthers of one flower to the high stigma of the other sort, and from the low anthers of the latter to the low stigma of the former; that the adjustments and lengths were such as to secure this cross-fertilization; and, finally, the intention was made the more manifest by experiments which proved that pollen of the one sort would act promptly and effectively upon the stigma of the other sort, but less so and sometimes not at all upon its own stigma.

The illustrations of this principle in various similar or analogous cases and the confirmation of it by evidence, mostly in the way of experiment, fill the larger part of this volume.

The conclusion is that there is some advantage in having two sexes in plants, as well as in animals; that this advantage is gained sometimes by having flowers of separate sexes in distinct plants, as in willows, but there with the disadvantage that half the trees are barren; or on different flowers of the same individual, as in pines and oaks, but still half the flowers are barren; or, finally, by the reciprocal fertilization of hermaphrodite flowers, and here with the economical advantage that all may be fruitful. Such is the economy of Nature. But she is multifarious in her economy. In the book on orchids Mr. Darwin shows how the same economy is subserved, and the cross-breeding made equally sure, in hermaphrodite flowers of one sort, the parts of which are so arranged that the pollen can seldom act at all except when transported by insects, while then in most cases it will be transported from one flower and from one plant to another. In these publications attention is directed to various different arrangements—"contrivances," as they are fittingly termed-for securing the general or the occasional cross-fertilization of flowers in a great variety of kinds. which were formerly thought to close-fertilize. And in the volume on the effects of cross and self-fertilization it is shown by experiments, more or less convincing, that such cross-breeding is beneficial. We might feel assured that it was from the manifold and elaborate arrangements which conspire to secure it. But, as these depend for success upon extraneous agencies—upon insects, winds, etc.—and are, therefore, more or less precarious, they are supplemented by other and seemingly contradictory arrangements for a certain amount of close-fertilization also.

Such are the topics of the book before us and of the related volumes of the series. Those who know of the author only through his writings upon evolution, and who look on these with misgiving or alarm, may yet share with us the interest with which we welcome works like these. To restore the idea of intention to its rightful place in natural history is no insignificant achievement. To open fresh fields of observation, which are accessible to all, old and young, in which new illustrations of curious contrivance and beneficial intention may be discovered in great variety by common observers, who have comprehended the principle and learned to use their eyes, is one of the latest and best contributions of science to education.

HARVARD COLLEGE.