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It has just been stated that plants do not (as far as is known) exhibit the phenomena of warning-colors or of protective resemblances; but it is true that the coloration of flowers, their perfume, and the presence of nectar l in them, are always of great service to the plant.
Sir John Lubbock, an English banker of the highest reputation as a naturalist, in his fascinating lectures, relates, among many careful observations, positive experimental proof that bees and wasps are attracted by bright colors, and that they prefer the same odors that men do. Every housewife knows that the smell of fresh meat or fish quickly attracts the large blue-bottle flies; while such odors as that of boiling fruit or of hot vinegar, not only attract flies, but bees, wasps, and hornets as well. I have seen the door and window screens literally swarming with these insects, about a kitchen where peaches were being scalded in spiced vinegar.
It is now proved beyond doubt that the color and odor of flowers enable them to utilize the services of insects while guiding them to the store of nectar inside. Flowers that have
1 Commonly (but wrongly) called honey: the latter is a manufactured uct, due to the bee.
2 Scientific Lectures, p. 31 (and in many other passages).
no nectar are, as a rule, neither bright-colored nor sweet-scented; while those that have it are usually attractive in one or both of these ways. Now, it has been found that such attractive flowers are dependent on insects to carry for them the fertilizing dust, or pollen, from one flower to another; and that, unless the pollen is so carried, few or no perfect seeds will be ripened by the plant. In any flowering-plant the production of seed depends on the transference of pollen from the male parts, or stamens, of the flower, to the female parts, or pistils; but it was until recently thought by most botanists, that any fresh pollen of the same species of plant would answer the purpose. This, however, has been disproved by the investigations of Darwin and others; and the fact, as stated in a preceding paragraph, that attractive flowers depend on insect-fertilization is now undisputed. On the other hand, such inconspicuous flowers as those of the grasses, rushes, and sedges, as well as of many foresttrees and other plants, either depend on the transference of pollen by the wind, or are capable of self-fertilization; that is, of using the pollen in the flower in which it is produced. It needs little calculation to show that the plant would generally be benefited in the struggle for existence by being adapted for insect-fertilization rather than for fertilization by the wind; since the former method economizes the strength of the plant by requiring less pollen to be produced, and also makes the result far more certain, thus giving a better guaranty for the preservation of the species. Out of the multitude of examples of the marvellous arrangements for securing insect-fertilization, described in such books as Lubbock's Scientific Lectures," and Darwin's "Fertilization of the Orchids,” a single case must suffice for the purposes of the present chapter. The flower of salvia, as represented in Fig. 8, is two-lipped in form. Its
Fig. 8. — Diagram of Flower of Salvia, and of its Stamens.
anthers, a, a, mature before the pistil, p, shown in A. A bee visiting any newly opened flower
of the salvia would become dusted over the back with pollen from the ripened stamens. These have their anther-cells pivoted to the filaments (B, f, f) in such a way that the insect, on entering the flower, must tilt both anthers into the position shown at C. In this position it will be noticed (Fig. 9, A) that they lie close
Fig. 9. - Salvia Flowers of Different Ages, one visited by a Bee.
pressed against the bee's back. Now, when she Alies to an older flower of the same species, the bee no longer finds the stamens in position, as in the former flower: they are shrivelled up out of the way, and their place is taken by the stigma (B, st). The position of the stigma is such that it will just brush the insect's back, and so rub off from it a little of the pollen brought from the former flower. How carefully the pollen is economized! And yet this is by no means as wonderful an arrangement of parts as is found in many orchids. But insects, while foraging for themselves, may be made to work for plants in ways quite different from those already explained. Mr. Wallace states that certain acacias with large hollow thorns, by means of the sweet pulp stored in these thorns keep a standing army of savage ants, which first feed on the pulp, and afterwards live in the cavity from which it was taken, still finding food on the tree, in the shape of honey-glands on the leaf-stalks, and of small fruit-like bodies, both of which seem to be much relished by the insect-guests of the tree. Mr. Belt (from whom Mr. Wallace obtains these facts) concludes, from his study of the case, that the ant-army is useful to the tree by protecting it from the leaf-cutting ants, which destroy great numbers of such trees as are not guarded against their ravages.