BY HARLAND COULTAS.

PROCESS OF FERTILIZATION.—The young seeds or ovules are contained in the interior of the pistil before the flower opens, and continue to grow until that time, but no longer, unless they are acted upon by the pollen of the anthers. The necessity of this process shows why it is that stamens and pistils are so constantly found in flowers, and why the former surround the latter so nicely as they in general do; and, even in circumstances which seem somewhat adverse to fertilization, still some admirable contrivance is always found to bring about the same end.

In some flowers, we meet with beautiful contrivances for securing the fecundation of their pistils. Thus, such as are erect have usually the stamens longer than the pistils, whilst in pendulous flowers it will be found that the pistils are the longest and the stamens the shortest. By this admirable relative adjustment, the pollen, in falling, comes into contact with the pistil. The Fuchsia, or ladies' ear-drop (Fig. 1), shows the character of this arrangement in a pendulous flower: p is the pistil, and s the stamens, which, it will be perceived, are much shorter, and situated above the pistil, in order that its viscid stigma or summit may receive the pollen as it falls out of the anther cells.

There are a few well-known instances in which fertilization is effected by certain special movements of the stamens. The stamens of the barberry spring to the pistil, if the lower part of their filaments is touched; and in Parnassia palustris, the grass of Parnassus, a rare and beautiful snow-white swamp flower, the stamens move towards the pistil in succession to discharge their polliniferous contents.

The flowers of the Kalmia latifolia, or mountain kalmia, a native evergreen, very abundant on the side of barren hills and the rocky margins of rivulets, are especially deserving of attention. The corollas of the kalmia are rotate or wheel-shaped, and have ten stamens, the anthers of which, before the flowers expand, are contained in ten little cavities or depressions in the side of each corolla, where they are secured by a viscid secretion. When the corollas open, the filaments of the stamens are bent back by this confinement of their anthers like so many springs, in which condition they remain until the pollen in the anther cells becomes ripe and absorbs the secretion. The anthers, becoming suddenly liberated by this means from their cavities, fly up with such force as to eject their pollen on the pistil. The slightest touch with the point of a needle, or the feet of an insect crawling over their filaments, is sufficient to produce the same effects when the pollen is mature. Fig. 2 shows, at a, the fully expanded flower with the confined anthers; at b, the flower after the anthers have discharged their pollen.

When the stamens and pistils are together in the same flower, it is designated as hermaphrodite, and complete; but, if the flower contains only one of these organs, it is termed unisexual, and, in this case, it is either male or female, according as it is composed uniquely of stamens, or male sexual organs, or of pistils, or female sexual organs. This separation of the sexual organs in flowers is of very frequent occurrence. The greater portion of our forest trees, and many herbaceous plants and shrubs, have unisexual flowers.

Sometimes the stamens and pistils are situated in separate flowers on the same plant. When this is the case, the staminate flowers are generally situated above the pistillate. The Indian corn exemplifies this arrangement. It is well known that the flowering panicle at the summit of the stem does not produce corn; these are the staminiferous flowers from whose anthers descend clouds of pollen on the threadlike pistils forming the silky tuft beneath. Without this pollen, the corn in the lower spike would not ripen; hence the evident design of nature in placing the pistillate below the staminate spike of flowers.

In forest trees, these unisexual flowers are usually borne on separate individuals of the same species, or the flowers on one tree are wholly staminate, and those on the other altogether pistillate. It must be obvious that such plants are still more unfavorably situated for fertilization. The great abundance of pollen produced compensates for the unfavorable situation of the flowers. The wind drives it far and near, and the air becomes sometimes so charged with it that rain, in falling, brings it down to the ground in considerable quantities, producing the so called sulphur showers of which we read in history. There is no doubt, also, that the bee and other insects in search of honey convey the pollen from the stamens to the pistils in unisexual plants.