Page:Popular Science Monthly Volume 37.djvu/395

This page has been proofread, but needs to be validated.
381
OBSERVATIONS UPON DOUBLING OF FLOWERS.

developed pollen. In the petunia the doubling of the flower is usually accompanied by a remarkable modification of the pistil—in short, a secondary flower is formed within the ovary. Botanists have long recognized an exceptional development of the floral axis which has been termed prolification. In this there may be a prolongation of the axis beyond the blossom, and the development upon it of ordinary foliage. The European larch furnishes a good illustration of this. Sometimes an ordinary leafy stem extends upward from the center of the cone for nearly a foot. In rare cases leafy branches have grown out from the i free or blossom end of pears, and buds and long branches have arisen from the center of a rose. In the petunia this prolification, if we may call it such, assumes the form of a small and much-contorted flower. Repeated examinations of normal flowers fail to show any unusual structure to the pistil. It is, therefore, associated with the doubling process in the petunia. Instead of the end of the floral axis, which terminates at the base of the single centrally situated pistil, remaining as such, it develops into another flower, and this within the ovary of the primary blossom. Just why we should have this peculiar form of prolification, or any, in fact, is not for us to decide. The ordinary forces which would construct a normal flower have been thrown into confusion, and retrograde metamorphoses and floral prolification have resulted. In fact, it seems evident that out of the substance ordinarily producing a capsule of petunia-seed has been formed in the same ovary an amalgamation of stamens, petals, and a rudimentary pistil. In short, the tendency to petaline display does not stop with the stamens, but invades the pistil, and transforms it as already described.

After doubling has once become established, and the tendency is an hereditary trait, it still remains true that surrounding conditions may favor or modify it. It is well known that among wild plants the absence of favoring surroundings will hasten the period of reproduction, and even augment the yield of fruit. With doubled flowering plants it may be that they strive toward the same end, but fall short because of non-reproductive tendencies developed in them by long-continued culture for their showy flowers only.

 


 
A relationship between the flora of eastern Asia and of eastern North America was pointed out, as to Japan, by Dr. Asa Gray thirty years ago. It has been illustrated since by discoveries of new species alike in both regions, but they have been for the most part unimportant herbs. Greater force is now given to the fact by the discovery, by Dr. Augustine Henry, that the Chinese and American tulip-trees are identical. The discovery is significant in that it gives evidence that the climates of eastern America and of China have continued to be alike since the Tertiary period.