in June. From these individuals are produced the sixth generation. The sexes now come together for the first time and after union lay their eggs on the witch-hazel. These eggs in turn hatch into the stem mother first described. The sixth generation are wingless forms and reach maturity in two or three weeks. Their eggs are laid about the middle or end of June and it is the young from these eggs that hatch about the time the flower buds are developing on the witch-hazel.

In this cycle of life is exemplified a remarkable case of parthenogenesis, or the giving forth by birth of individuals from an unimpregnated female. The virgin female here has the latent power to give birth to live larvæ, and each generation, from the first to the sixth, has similar power. All the adult females have some easily recognizable differences in structure, and the whole cycle starts over again each alternating year, commencing with the egg.

Cockerell has advanced the idea of accounting for the evolution of galls on the theory that the secretions of certain earlier mining insects caused a swelling to appear, where the larvæ lived, on which excrescence they fed. "It is easy to see that the greater the excrescence, and the greater the tendency of the larvæ to feed upon it instead of destroying the vital tissues, the smaller is the amount of harm to the plant. Now the continued life and vitality of the plant is beneficial to the larvæ, and the larger or more perfect the gall, the greater the amount of available food. Hence natural selection will have preserved and accumulated the gall-forming tendencies as not only beneficial to the larvæ, but as a means whereby the larvæ can feed with least harm to the plant. So far from being developed for the exclusive benefit of the larvæ, it is easy to see that allowing a tendency to gall-formation, natural selection would have developed galls exclusively for the benefit of the plants so that they might suffer a minimum of harm from the unavoidable attacks of insects." 1

The great number and variety of galls agree in presenting a more or less elaborate structure, says Romanes, which is not only foreign to any of the uses of plant life, but singularly 1 Entomologist, March, 1890.

2 "Darwin and After Darwin," Part I, p. 293.

and specifically adapted to those of the insect life which they shelter. Yet they are produced by a growth of the plant itself when suitably stimulated by the insects' inoculation — or, according to recent observations, by emanations from the bodies of the larvæ which develop from eggs deposited in the plant by the insect. Evolution may have acted through the insects, for "it may very well have been that natural selection would ever tend to preserve those individual insects, the quality of whose emanations tended to produce the form of galls best suited to nourish the insect progeny; and thus the character of these pathological growths may have become ever better adapted to the needs of the insects."

THE GUESTS OF THE WILD BERGAMOT

In late summer the wild bergamot often grows in clumps covering large patches of ground, in pastures, fields, and roadsides. Where these flowers are thus assembled, bumblebees and butterflies are often seen drinking the sweets. It is not until one carefully studies the flowers of this plant, together with its insect guests, that some interesting facts are brought to light concerning adaptations. In the first place, the tubes of the flowers are seen to be quite long, indicating that they are more nearly adapted for long-tongued insects such as butterflies and moths.

According to Robertson, the peculiar form of the tube, the two-lipped corolla, and the position of the stamens and style, indicate that the flower is a modification of a flower originally adapted to bumblebees. The level-topped heads, the erect corollas, the exposed organs, and rose color make it an attraction for butterflies,—the principal guests. Pammel says that the Iowa flowers, as well as those of Wyoming and Colorado, are frequently visited by bumblebees, though butterflies are not uncommon on the flowers in Iowa. In Michigan, I have found that the bees far outnumber the butterflies as frequenters of the flowers.

These flowers are probably in the process of active changes from bee flowers to butterfly flowers. The change is, perhaps, somewhat hindered, owing to the different insect visitors they

have as guests from year to year. One species of butterfly which is frequently found on the blossoms is the pretty little yellow species, Terrias lisa, which is shown in the illustration, just as it is about to alight on a flower. As the larvæ of this insect feed on a species of cassia and on clover, the visits of the butterfly to the wild bergamot are for nectar. It must be admitted that structures of flowers often appear to have indifferent characters which are difficult to account for on the ground of natural selection. It is, however, more often our ignorance of the complex life as well as a quantitative analysis of variations of a flower that lead us astray in interpreting these structures.

THE SEASONAL PROCESSION OF THE
FLOWERS, INSECTS, AND BIRDS

ARDLY can we realize the changes being wrought in the woods and meadows unless we keep in close touch with the varied conditions of nature. On August twenty-second, after a night of rain, I find the following summing up of the day's reflections: The flowers of the wild bergamot, which a few weeks ago appeared in their best colors, are now fast fading. It is rare that a per

fect, fresh flower can be found unless it may be one growing in some shady spot. With the going out of the bergamot are contrasted the cardinal flowers, which are now

The Troilus Butterfly (Papilio troilus) visiting the Cardinal Flower (Lobelia cardinalis). This butterfly, along with the ruby-throated humming-bird, aids in the cross-fertilization of this flower. It mimics the butterfly Pharmacophagus (Papilio) philenor on both upper and lower wing-surfaces. See

colored frontispiece.