Page:Popular Science Monthly Volume 39.djvu/352

338 seed. Dr. Gray has likened the plant to the fabled phoenix, which, consuming itself in giving birth to its offspring, literally rises from its ashes.

All the parts of a complete and perfect flower are, morphologically speaking, modified leaves. It can often be observed that true leaves pass insensibly into bracts. These in turn pass into sepals, and these again into petals. Sepals, being as a rule green, can be more easily seen to be modified leaves than petals. The last are usually colored, and the fact is not so noticeable. Yet, in the flowers of the cacti, the line between the outer bracts and the sepals, and between these and the petals, can not be drawn, for they pass imperceptibly into each other. In the Nymphæa (water-lily) there are numerous rows of petals, and a gradual change can be traced from the outer row of petals into stamens. First at the tip of a petal are developed two small lobes, one on each side. These lobes enlarge as the center of the flower is reached, and at last a fully formed anther at the top of a slender filament is the result. All the various stages through which the stamen has passed are visible in the rows of petals.

According to Mr. Grant Allen, the original and primitive flowers were made up of stamens and pistils only as the essential organs of the flower; and the petals and sepals are but stamens modified by insect agency. Now, whether petals are regarded as modified stamens or stamens as modified petals is immaterial. There is nothing to prevent the adoption of both views. The stamens must, in the first place, have been leaves; for it often happens that ordinary leaves are found bearing pollen grains on their edges. So, too, the anther is to be regarded as the modified apex of a rolled-up leaf. As the flowers became, in the course of time, more and more suited to insects, some of the stamens were doubtless changed back into leaves in the shape of petals and sepals, while at the same time the true leaves of the stem may have been changed into bracts of various sorts.

There will be noticed, on the examination of any ordinary stamen, two principal parts. One is the long, slender stalk or filament, and the other is the knob at the end, or the anther. The filament, says Sachs, is to be regarded as the staminal leaf. The anther is made up of two lobes, situated at or near the apex of the filament, one on each side, and separated by a prolongation of the filament known as the connectile. In these two lobes the pollen is developed. Sachs says that "the formation of . . . the pollen grains of phanerogams always takes place by the division of the mother-cell into four parts." This division takes place as follows: In the process of growth of the original mother-cell, the nucleus becomes divided into two parts, each soon forming the center of a new cell. These two again each divide and finally