[page] 155

DARWIN ON FORMS OF FLOWERS*

THIS book, of about the size of the preceding one, On the Fertilization of Orchids by Insects, or of that on Cross and Self-Fertilization, is not so readable or generally interesting, partly because its bearings upon Darwinism are remote and incidental. Nor would the title give to most readers much idea of the contents. But to those who can appreciate exquisite adaptations in nature for their own sake, and see in these adaptations evidences of a superior wisdom, the story which this book tells will be instructive.

All are familiar with the fact that while some flowers are both male and female, others, such as of oaks and birches, have the two sexes in different flower-clusters on distinct branches, and still others, like poplars and willows, bear them on different trees, these depending upon the winds or sometimes upon insects to carry pollen from the one to the other. But few are aware that there are many plants bearing perfect and complete blossoms, quite alike as to all but the stamens and pistils, and these different only in relative length and the nature of the pollen; and that this length is so regulated as to ensure the transport, by insects, of the pollen of the long stamens of the one to the long pistil of the other, and from the short of the one to the short of the other, so as to bring about reciprocal cross-fertilization; also that the pollen of each sort is nearly impotent as to the pistil of its own flower, but prepotent upon that of the other form. Through this arrangement such flowers retain all the benefits as to crossing, of those with separated sexes, along with the great advantage that both forms are seed-bearing and prolific.

The hop flowers are in separate sexes; so it is necessary to plant some sterile vines among the fertile sort, which alone produce the cross. But this "dimorphism" subserves the same end with greater economy. We are not sure that this case, of long and short stamens and pistils, occurs in any plant cultivated for man's use; but it is exemplified in some of our familiar wild flowers, such as Houstonia and Partridge-berry.

Two-thirds of the present volume is devoted to the complete elucidation of this sort of reciprocity. The book on Orchids shows that the same result, in the way of preventing breeding in-and-in, is attained with only a single sort of perfect flower; and in the book on Cross and Self-Fertilization, the benefit of all such crossing is explained and proved. So it might well be inferred that cross fertilization is the plan in the vegetable kingdom, or, at least, that it plays some important part.

But, strangely enough at first sight, there is a considerable number of plants which bear, along with others capable of being crossed, a set of flowers which must be close-fertilized, and which are evidently constructed for this very purpose. Truly, "great and manifold" are the works of—Nature, as we are pleased to phrase it, and if not "past finding out," they are far from being all found out yet.