POLLEN. The pollen of plants is the fecun dating dust or minute grains of organized ferti lizing matter which, falling upon the pistil of the flower, throws out hair-like tubes, which pene trate through the' whole extent of the vascular tissue of the pistil, and reaching the ovules, fertilize them, thus rendering them capable of perfecting the seed, and reproducing plants of their own kind. The pollen, therefore, repre sents the male element in plant life. The male and female organs (stamens and pistils) are some times in the same flower, as in the apple. These are called perfect flowers. When the stamens and pistils are on different flowers and on the same plant, as in the white, oak, they are called monceelaus. When in different flowers and on different plants, as on hemp, they are called dons. How the fertilization in different plants is accomplished, Mr. Horace Piper, of Maine, relates as follows, taking perfect flowering plants,moncecious and &melons plants, to illustrate the three classes: In the first class the pollen is conveyed from the anthers to the pistils in some cases by actnal contact of the two organs, as in the potato (Solanum tuberosum); in others, by the elasticity or spring of the stamens at the time the anthers emit the pollen, by which action it is scattered on the pistils, as in the mountain laurel (Kalmia lat(folia); and still in others by the posi tion or length of the stamens, being above or hanging over the pistils, and, therefore, requir ing no accidental means to fertilize the plant. In the second class the staminate flowers are generally situated above the pistillate, and over them on the same stalk, so that the pollen falls upon the pistils by the mere force of gravity, as in Indian corn, in which the part commonly called the spindle contains the staminate flow ers, and the ears the pistillate. In the third class the staminate flowers are on one plant, and the pistillate on another; therefore, the pollen must be conveyed by some artificial means from the stamens to the pistils. This is readily accomplished by the wind or insects. The grains being light and very numerous, are easily wafted by the breezes and severe winds in sufficient numbers, and to the necessary distances, to accomplish the desired object. But, lest this mode of conveyance should prove inadequate, nature has provided another security just referred to, namely, the transmis sion by insects when in search of honey for their food. Passing from the flowers of one plant to
those of another, often to great distances, they carry the pollen which has adhered to their legs and bodies, and deposit it on the pistils of the flower of another plant, which is thus rendered fertile, and is as certain of producing fruit as if the pollen actually fell upon the pistils from the anthem of the same flower. In this way we may account for the fact that some trees of this class though thrifty and producing an abundance of flowers, do not bear any fruit. It is simply because there is no staminate plant sufficiently near from which pollen may be conveyed by any of the means above to the insulated plant. And, again, the plant may be so far distant as not to admit the pollen to reach it at all, or only on some extraordinary occasion, and, therefore, it ,would produce fruit only when such accident should happen to occur, which might never be. We have a very curious instance of the manner in which fertilization is sometimes effected in this class of plants in the case of the Vallisneria spiralis, in which the flower of the staminate plant detaches itself from its stalk and swims to its mate, attaches itself to it, and remains until it becomes fertilized, when both flowers wither and sink beneath the surface of the water in which they grew, the one to perish, and the other to mature seeds, and sow them on the muddy bottom below. As illustrating the action of pollen, Broigniart and others think .that when the hair-like tube of the pollen-grain passes through the orifice in the coatings of the ovule, and reaches the nucleus, or embryo sac, it emits a spermatic or plantlet germ, which passes through the wall of the embryo sac and enters the ger minal vesicle contained in it. The vesicle cor responds to the germinal spot, or vesicle, in the egg of birds, and the ovum of mammiferous animals. The germ remains in the vesicle, and finally becomes the embryo fully developed into a plantlet, as may be seen in the bean and other seeds. These tubes sometimes grow to great length, and are many days in penetrating the p whole length of the pistil. Indian corn will fur nish a good illustration. The pistils of this plant, which are commonly called the silk, grow to the length of ten or twelve inches, and yet these slender pollen-tubes penetrate the whole distance from the point where they come in con tact with the pistils to the nucleus of each rudi mentary seed.