Page:Popular Science Monthly Volume 9.djvu/793

Rh Dry Thunder-Storms.—A correspondent in Oregon, Missouri, communicates some observations on weather phenomena, especially upon the influence of forests on rainfall. "When the earth has become dry, parched, and very warm, on occasion of thunder-storms, I have often," he writes, "noticed for hours, while it was thundering overhead, the mist, falling from the storm clouds, to roll back, after nearly reaching the earth, in the form of lighter vapor. I think this rain, or mist, in falling, passed down to the stratum of very hot air on the earth's surface, and became a steam, large volumes of white vapor forming suddenly and rolling back and up. Now I am confident that, if the earth had been shaded by trees, this rain would have fallen on the ground.

"This phenomenon can be seen here every hot, dry season. It has, no doubt, escaped the attention of all but very close observers. Mine was called to it by a question asked while one of these dry thunderstorms was prevailing—a common thing—dry thunder-storms—thunder rattling overhead, but not a drop of rain falling. The white mist is not easily observed overhead, where all is light; but opposite to the sun, under the dark storm-cloud, it is very plain, and must attract attention."

Fertilization of Plants.—Mr. Thomas Meehan discovers in the "sleep" of plants an agent in their self-fertilization. The fertilization of the common Claytonia Virginica had been somewhat of a mystery to him, as, in view of the prevailing theory of cross-fertilization by insect agency, this plant ought not to be a self-fertilizer; but from repeated observation he was satisfied that no insects had visited plants that had yet seeded abundantly. Watching the process of fertilization, he found that the stamens on expanding fell back on the petals expanded during daylight. At night, when the flower closed, the petals drew the anthers up in close contact with the pistils. Cross-fertilization could be accomplished by insects if they visited the flower, but they did not, and actual fertilization only occurred in this way. In many cases, especially late in the season, the stamens recurve so much as to be in a measure doubled up by the nocturnal motion of the petals. The anthers were not drawn into contact with the stigmas in these cases, and, as a result, the flowers were barren.

In the Ranunculus bulbosus, our common buttercup, in the evening following the first day's expansion of the young flower, the immature anthers and the young stigmas would be found covered with pollen-grains. The inference would generally be, that this had been carried there by insects. But, as he had been especially on the lookout for insects as visitors to the buttercup, and feeling sure that none of any consequence had been to them, he examined these flowers carefully, and found that, on the first expansion of the flower, a single outer series of stamens burst their anther-cells simultaneously with the expansion of the flower, and, by contracting the cell-walls, ejected the pollen to the smooth petals, from which it easily fell to the immature anthers and stigmas, when the flower closed for the night.

Knowing that another species of buttercup, the Ranunculus abortivus, had fixed spreading petals which did not close at night, and which, though with comparatively large nectariferous glands full of a liquid secretion, was wholly neglected by insects, and yet had every flower seeding profusely, he was anxious to find, in view of his other discoveries, how these were fertilized. Visiting a wood after twilight, to ascertain if any nocturnal insects visited them, he found that, though the petals did not close at sundown, the slender pedicles drooped, inverting the flower, and in this way the pollen found its way from the petals to the stigmas without any difficulty whatever.

Functions of the Root-Hairs of Plants.—In an article published in the Gardener's Monthly, Prof. B. C. Halsted points out the functions of the "root-hairs" of plants. These so-called root-hairs are thread-like structures, consisting of elongated surface cells of the root. These hairs absorb water out of the soil either by capillary attraction, or by the process of diffusion, or by osmotic action. It is a well-known fact that porous bodies absorb liquids to a greater or less extent. A dry cloth hung so that one