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Page:Popular Science Monthly Volume 32.djvu/204

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THE POPULAR SCIENCE MONTHLY.

forms, which have each been considered by confirmed "splitters" as distinct species. The first (P. sarmentosa, of Muhlenberg) grows for the most part on very dry soil, and like most plants of arid situations runs largely to pronounced hairiness; for it is a general rule that water-haunting kinds are smooth and glabrous, while dry or desert types are intensely hirsute (the reason for this wide distinction, though well known, would carry us too far away, this morning, from our main subject). The second form, erected by Michaux into a separate species (P. simplex) but reduced to subordinate rank as a variety by Torrey and Gray, belongs to moister soil or to deep meadows, where the lush grass prevents evaporation; and this type grows less hairy and greener, and attains a larger and more luxuriant stature. The two forms differ also in other ways, strictly dependent upon their differences of locality. Sarmentosa, the dry type, creeps squat upon the ground, as if to avoid the sun, and sends out long, rooting runners in every direction after the fashion of the strawberry-vine; whereas, simplex, the moister kind, has ascending stems, which rise in competition among the grasses around them, seldom if ever creep, and never produce summer runners. Again, sarmentosa begins to blossom early, and ends early—April to July in the latitude of New York; while simplex comes and stops a month or so later at either end—May to September in the same district. In other words, the dry type flowers early in spring on its basking banks, but retires from the scorching heat of your American summer; while the moist type begins later in its shady habitat, but is less affected by the droughts of August.

Curiously enough, our common European cinque-foil (P. reptans), the exact analogue of your American plant, and fellow-descendant of the self-same pre-glacial ancestor, has also two well-marked forms usually considered as distinct species, but merging into one another by imperceptible gradations. The parent-type (reptans proper) grows in rich pastures or meadows, and answers best to your variety simplex, though it sends out long, creeping stems which root every now and again at the nodes; it has five large petals to each blossom, and the flowers are identical with those of the Canadian cinque-foil. But on open moors, heaths, and dry places, we have a smaller, closer, and more creeping form, the tormentil (P. tormentilla); it is silky-hairy, like your own sarmentosa, and its upper leaves have often only three leaflets instead of five, thus reverting to the ancestral type of foliage, when the plant was rather a tre-foil than a cinque-foil. But oddest of all, the small flowers have only four petals, arranged like a Maltese cross; whereas all their congeners have their full complement of five, in accordance with the old central plan of the entire rose family. Still, the first flower of all on each stem, produced when the plant is in its vigorous youth, has occasionally five petals; a reversionary fact of great interest. The tormentil has also an intermediate variety of its