Page:Popular Science Monthly Volume 16.djvu/292

278 the old editions, structural and physiological botany were considered together. There was no attempt to deal with them separately. But the present volume is specially devoted to structural botany, and leaves out physiology as far as possible. This difference is really greater than at first appears. Although structural botany was given along with physiology in the old editions, yet physiology was the only division of the science that was really learned from its pages. Of course, this was not intended by the author; but, with the human mind what it is, and the public schools such as they are, no other result was possible. When this work first appeared, and for long years thereafter, studying objects was undreamed of in our schools; lesson-learning was their sole occupation. But a descriptive science can not be learned from the pages of a book. Physiology could be acquired by the prevailing method, since it takes little account of the differences among plants, and would be much the same if the vegetable world consisted of only one species. The impression made upon pupils by the descriptive portions of "Gray's Class-Book" was so slight that, to the average student, the science of botany and the physiology of plants were about the same thing.

And so it happened that class after class of our youth left school complacently thinking that they knew botany, but with only the merest book-smattering concerning the classification of plants. Of course, if the forms and modifications of the organs of plants were not regarded, there could be little occasion for glossology; and, by the neglect of both organography and glossology, the sketch of the natural orders at the end of the volume was unintelligible. This could only be understood when the actual features of a large variety of plants were familiar to the mind, and the memory was also furnished with the exact terms applied to them. Educationally considered, therefore, this chapter of illustrations of the natural orders, covering more than a hundred pages, was little better than waste-paper.

The order of publication now adopted, which presents structural botany by itself at the outset of the study, will compel the teachers of botany to change their practice, and make the study of plants by direct observation a serious business. For, interesting and fundamental as is the physiology of plants, the discoveries of the last twenty years have rendered their morphological study more captivating still, so that the interest of the science reaches its highest point in systematic botany, or classification on the basis of genetic relationship. But the only possible admission to this delightful portion of the subject is through such a genuine knowledge of the contents of the present work as will come from wide and careful observation of living vegetable forms.

Another noticeable change in this treatise is the substitution of the doctrine of the development of species by natural selection for that of the special creation of species, which was taught in all former editions. The fifth was published in 1857, and Darwin's work on the "Origin of Species" did not appear until 1859. The new direction given to inquiry in natural history by this work, and the copious literature of the subject which followed it, have profoundly altered the aspects of biological science. The old system of comparative anatomy, which was based upon the doctrine of special creations, has given place to the modern science of morphology; which, from being, before Darwin's time, merely a descriptive study of forms, has become an analytical science of form, pervaded throughout by the principle of descent with variation. The following extract from his chapter on "The Principles of Classification" will sufficiently indicate the present attitude of Professor Gray toward the question of the evolution of species:

The theory of descent, that is, of the diversification of the species of a genus through variation in the lapse of time, affords the only natural explanation of their likeness which has yet been conceived. The alternative supposition, that all the existing species and forms were originally created as they are, and have come down essentially unchanged from the beginning, offers no explanation of the likeness, and even assumes that there is no scientific explanation of it. The hypothesis that the species of a genus have become what they are by diversification through variation is a very old one in botany, and has from time to time been put forward. But, until recently, it has had little influence upon the science, because no clear idea had been formed of any natural process which might lead to such result. Doubtless, if variation, such as botanists have to recognize within