such as the wild columbine, eject their small seeds by the bursting open of their capsules. Wallace intimates a suggestive fact that dominant groups of our large forest trees, such as oaks and beeches, are among the most ancient of known dicotyledonous plants, going back to the cretaceous period with little change of type, so that it is not improbable that they may be older than any fruit-eating mammal adapted to feed upon their fruits. The attractive colored fruits, according to Grant Allen, on the other hand, having so many special adaptations to dispersal by birds and mammals, are probably of more recent origin. Wallace maintains, "The apple and the plum tribes are not known earlier than the miocene period; and although the record of extinct vegetable life is extremely imperfect, and the real antiquity of these groups is no doubt very much greater, it is not improbable that the comparative antiquity of the fruit-bearing and nut-bearing trees may remain unchanged by further discoveries, as has almost always happened as regards the comparative antiquity of animal groups. At the present time adaptation "is precisely one of the things evolutionists are trying to find the causes or causal factors of. But nevertheless the adaptability of life stuff, its plasticity and capacity of advantageous reaction, is, to many biologists, a fundamental fact in organic nature, like gravitation or chemical affinity in organic nature; a thing basic and inexplicable, and in itself a factor whose consequences are to be determined but not further to be questioned as to their cause." ! FLOWER AND INSECT ADAPTATIONS Lubbock says that "not only have the form and colors, the bright tints, the sweet odors, and the nectar been gradually developed by the force of an unconscious selection exercised by insects, but even the arrangement of colors, the shape, the size, and the position of the petals, the relative position of the stamens and pistil are all determined by the visits of the insects, and in such a way as to assure the great object (fertilization) that these visits are intended to effect." 1 Jordan and Kellogg, "Evolution and Animal Life," p. 56. Many facts have been brought forward to prove that this relation actually exists, but not entirely on the assumption laid down by Lubbock. Recent studies by Bouvier, on the "Relation of Bees to Flowers," are summarized as follows: Nectar and nectaries are certainly intended primarily for the plant itself and do not prove an adaptation of the flower to insects. The colors and perfumes of flowers may be, perhaps, the result of such an adaptation, but in any case they strongly attract anthrophilian insects, signalling to them the presence of booty. In many cases, if not all, the complicated forms of the flowers must be attributed to the adaptation of flowers to their visits. It is almost unanimously conceded nowadays that Mellifera (or bees), at least in so far as their collecting apparatus is concerned, are beautifully adapted to the flowers, but, despite the fact that practice has shown that plants are in every way more plastic than animals, it is still strongly disputed that flowering plants have adapted themselves to bees. "If there does not exist any reciprocal modification," says Bouvier, "between the Mellifera (bees) and the flowering plants, it is not at all necessary to suppose that one group has been modified for the benefit of the other. Each has evolved on its own account." Explained thus, the many objections to the theory of reciprocal adaptation are overthrown. The bee has but one object, the pursuit of food, and all things which aid him in it are welcome. Usually, the plant profits thereby; sometimes it suffers. On the other hand, the plant seeks only to assure its propagation and all its modifications tend toward that goal. M. Gaston Bonnier quotes Claude Bernard as saying, "The law of the physiological finality is in each individual being and not outside it; the living organism is made for itself; it has its own intrinsic laws. It works for itself and not for others." Darwin, Müller, Lubbock, as well as others, have written detailed accounts of the adaptations of flowers to insects.1 During the visits of insects to flowers for the purpose of obtaining secretions of nectar and pollen, they involuntarily carry the pollen of one flower to the stigma of another, and thus 1 For a discussion of this subject consult Wallace, "Natural Selection and Tropical Nature," p. 400. effect cross-fertilization. Darwin was the first to demonstrate that the vigor and fertility of the next generation of plants were greatly increased by this process. It was, moreover, this discovery that led to researches which disclosed the most wonderful and complex arrangements that exist in flowers, all having for their object the prevention of constant selffertilization; but that pollen shall be carried, either constantly or occasionally, from the flowers of one plant to those of another. There was thus established the fact that the arrangement, length, and position of all the parts of the flower have a definite purpose, though a great variety of ways exist by which this same result is obtained. Open cup-shaped and quite regular flowers, in which it seems inevitable that the pollen must fall on the stigma and produce constant self-fertilization, are often prevented from doing so by a physiological variation. In these cases the anthers, continually emitting their pollen, wither either a little earlier or a little later than the stigmas of the same flower or of other flowers on the same plant when in the best state to receive it. As individual plants differ somewhat in the time of flowering, the pollen of one plant would often be conveyed by insects to some other plant whose stigmas were in a proper condition to be fertilized by it. Variations occurred in first one part, then in another, which have resulted in various adaptations for insect fertilization. Odors are developed as an attraction or guide to insect fertilization. Inconspicuous flowers are often possessed of strong, sweet odors, to be detected some distance away, while very showy flowers are seldom thus provided with scents. White flowers are usually exceedingly sweet perfumed. They are mostly fertilized by night-flying moths. The grouping of flowers so that they attract insects is often of considerable advantage. They are often conspicuously displayed in a broad flat top, such as is exhibited in the elderberry and wild carrot. These groups are made up of many individual flowers. Then there is the grouping shown in those of the lilacs and horse-chestnut. Again, we witness them closely packed together in tiny florets forming dense heads, as in the clover and all the Compositae, and in these the marginal florets are modified into rays such as shown in the daisy, aster, and sunflower. Bees are much more of a factor in fertilization in the temperate zone than butterflies. It is a general rule that flowers fertilized by the latter are much more conspicuous than those fertilized by bees. It is generally the case that the time of blossoming of these plants corresponds with the appearance of certain insects and in a few cases adjusted to the time of arrival of the ruby-throated humming-bird. It has been asserted by Grisebach come larger and more richly as, by the increasing length become rarer, and their coöpof fecundation is exposed to chances." 1 WHY THE NECTAR GATHERERS Na warm sunny day in the in blossom affords a centre of attraction for many insects. The sweet perfumed blossoms are scented far and wide by a host of busy little wanderers that come and congregate there. Such insects as the bumble and the honey bees are seen hanging to the pendent flower clusters, drinking the honey, while on the surface of the leaves many small flies play in the sunshine, and now and then take their lunch from the flowers. Argynnid and skipper butterflies participate in the grand convention of life. Species of bees, flies, and wasps collectively fly out into mid-air about the blossoms at every stir of the limbs and foliage. The birds, too, become aware of this meeting 1 Wallace, in "Natural Selection and Tropical Nature," p. 407. ground, and while viewing these sights, a Baltimore oriole snaps at some selected winged morsel. Like the mulberry tree in its attraction for birds, so the linden tree, in full blossom, is a delight to the senses of insect life, causing them to divide their attention between it, the chestnut, and the elderberry, which all blossom at the same time. Near one of the large basswood trees, where a view may be gained into its upper branches, the floral display alone, with its treat of perfume, is sufficient attraction; but, coupled with the harvest of insect visitors, one may easily spend a profitable hour contemplating the wonderful view, and adding something to the meaning of this great activity. On examining the flowers of the basswood, the honey is found secreted and held in the hollow sepals. "The petals and sepals are overtopped by the numerous stamens which curve outward so that insects can only alight on the anthers, or on the stigmas and the space between them. The possibility of self-fertilization is almost excluded by the stamens remaining bent outward to the last, while the pistil occupies the axis of the flower; only rarely is a flower met with in which an anther has become curved inward to touch the stigma." 1 The honey is only accessible to insects with short tongues. As none of the bees visiting the basswood blossoms had pollen in their baskets, Müller concluded that these insects visited the flowers for the honey and not for the pollen. There is an explanation of the cause of the diverse forms of insect frequenters to the basswood blossoms if we remember the observations of Knuth: "First, the more specialized a flower i.e., the more complex its structural arrangements and the more deeply seated its nectar the less are its insect visitors indiscriminately drawn from the entire insect fauna of a district, and the more do they belong to one or several similar species adapted to pollination. Secondly, the flatter and more superficial the position of the nectar, the more varied are the visitors in different regions, and the more are they indiscriminately drawn from the entire insect fauna of the region in question." 2 The basswood blossoms, shown in the plate illustration, 1 Müller, "Fertilization of Flowers," p. 146. "Handbook," Vol. I, 1906, p. 196. |