For reasons that will be enlarged upon in another chapter, all of these great groups of plants must be considered as of simple structure, some, like the pines, relics of a remote past when no flowering plants, as we know them to-day, existed on the earth. In any event the reliance upon the wind is certainly hazardous, and while it of course insures nearly universal cross-fertilization, it may well result in scanty fertilization or, in exceptional cases, complete failure of it. Quite obvious also is the amount and direction of the wind in the process, for in very open and windy places grasslike vegetation, or at least a predominance of species fertilized by wind, is likely to be found, rather than those plants that rely upon insects, that, unable to stand the full force of the wind, seek more sheltered places. While such a thing is not the cause of prairies, or the predominantly grasslike vegetation along sand dunes, or the exclusive spruce forests of the bleak and windy north country, it unquestionably aids in maintaining the often exclusive nature of such pure associations of plants. Over thousands of square miles on our own great plains or on the steppes of Russia, both subject to violent winds, the great bulk of the vegetation is wind fertilized. It could hardly be expected that pollen, once in the grip of such a wayward and shifting thing as the wind, should not be wasted in great quantities. This is particularly true of pine trees, which at pollen time may often be seen giving off golden clouds of dust, of which perhaps 95 per cent is wasted. WATER AS AN AID TO FERTILIZATION Those submerged aquatic plants upon which neither the winds nor honey-seeking insects can work the magic of cross-fertilization, seem to be about the poorest equipped for perpetuating their kind through impregnation of their tiny flowers. And yet, for at least two of them, which will be described presently, the process is accomplished by an adaptation of their mode of life to their watery environment that seems incredible. These two have been selected as illustrating two peculiar adaptations in the weight of pollen or pollen-holding flowers that is common to some other submerged aquatic plants. In one the male flower, or pollen from it, with the very nicest adjustment of function to environment in all the realm of the plant world, is just of the right specific gravity to float to the surface with dramatic suddenness and perfectly timed effectiveness. In the other the pollen is _just_ enough heavier than the water to float betwixt the surface and the bottom, so that at the proper moment it is where it can fulfill its destiny.