All along its under-water front the obscure under-water weeds grow up and die year after year, generation after generation, forming fertile banks of beautiful soft mud, into whose lower depths the great thick rootstocks of the pond-lilies push, and in which the fibrous roots of the tape grass, the fresh-water eel grass, find a hold. The growth and decay of these, with the water shield, with its jelly-protected foliage, the yellow dog-lily, and in lesser depths the bulrush, add to the growing bank as coral insects grow and die in tropic seas, until it is near enough to the surface for the pickerel weed to find roothold. Then indeed the bog steps forward with vigor, for the pickerel weed is its firing line. All summer you shall see its blue banners flaunting gayly in the southern breezes, tempting the land-loving bumble-bee to sea, calling the honey-bee from the mile-distant hive, and offering rest and luncheon to a myriad lesser insects, all with genial hospitality. Its serried millions in close ranks breast the waves in a broad blue line from one end of the bog to the other, a half-mile or so. Behind these are shallow pools, where again you find the white water-lilies. Here they bloom in enormous profusion from late June until early September, reaching their grand climax during late July. On such a day, standing in the boat at the southerly end of the bog, counting those within a given space and multiplying, I estimated that there were ten thousand of the fragrant white blooms in sight. Twice as many more were hidden by bulrush and pickerel weed. On Sundays and holidays boatloads of trolley trippers paddle and push among them and carry them off by the hundred, yet they make no mark on the visible supply. The decay of the leaves and stems of these add to the under-water foothold of the bog, but after all it must be the reedy stems, sagittate leaves, and interwoven roots of the pickerel weed that are its main foundation. Steadily seaward over the foundation thus laid progresses the long, definite front of the saw-edged marsh grass. Once it interlocks its roots along the mud surface formed for it, it leaves no room for the freer-growing denizens of the shallows. In among the marsh grass grows no flaunting flag of pickerel weed, no pure white nymphæa sends forth its rich odor. Only the bog cranberry may hold its own in any quantity against the throttling squeeze of those grass roots. Where these grow is the high sea of the bog, its waves rising and falling in the free winds. Yet, just as pickerel weed and water-lily give way before the advance of the marsh grass, so it in turn falls on the landward side before the advancing hosts of the swamp.