the stigma. The fovilla, or the mucilaginous fluid filling the grain, proceeds by endosmose into the tube, and thence to the ovule. An effort has been made to disprove the statement that pollen tubes penetrate the style, and so fertilize the ovules; but the great mass of evidence, and the statements of many observers who have seen the tubes in contact with the ovules, indicate that the tubes sent out from the pollen grains do penetrate the style, and then are brought into contact with and fertilize the ovules.
It is a strange fact that pollen grains are often entirely inoperative on the stigmas of the flowers that produce them. It has been found by many experiments that, when certain flowers are inclosed in nets, and insects thus excluded from them, if the pollen be applied to the stigma of the flower that produces it, the capsules never set seed; but, if the pollen of another flower be
Fig. 8.—Pollen on Stigma of Antirrhinum mojus. (After Brongniart.) applied, then the stigma is fertilized and seed is produced. In the California poppy (Eschscholtzia) there is a remarkable instance of this. Fritz Müller, in Brazil, found it completely sterile with its own pollen. Darwin, in England, found that even with the Brazilian stock of Müller he could get only a few seeds. Thus the sterility appears to depend on other things besides the pollen, the climate, perhaps, having some effect. Sometimes, too, it happens that, if the home pollen grows, and then foreign pollen be applied, this last grows faster and crowds out the first sort.
The immense number of pollen grains produced by a single flower apparently militates against the saying that Nature allows nothing to be formed but what is needful. It seems, indeed, a vast waste of material to have such a multitude of grains when so very few would answer the same purpose. In a single flower of the peony there are about three and a half million grains; a flower of the dandelion is estimated to produce nearly two hundred and fifty thousand; the number of ovules in a flower of the Chinese wistaria has been counted and the number of pollen grains estimated, and it is found that for each ovule there are seven thousand grains. While few fall below the thousands, many rise far above the peony in point of numbers. These are the wind-fertilized flowers, and here Nature must provide for an immense loss of material. Darwin says that "bucketfuls of pollen have been swept off the decks of vessels near the North Ameri-
