The swamp-thistle, with flower-tubes longer than those of its Canadian cousin, has a smaller circle of insect friends, and the common thistle, with still deeper florets, is more exclusive still. But all varieties are forced to receive unbidden guests, for ants dearly love nectar, and they are enterprising, persevering, and chronically hungry. If they can get into the purple tubes they will gormandize the sweets there, so that the robbed florets will have no inducement to offer to butterfly or bee, and it is extremely unlikely that an ant will pay for her refreshments by carrying the pollen where it ought to go, to another flower of the same species.
So there has been a warfare, summer after summer, for no one knows how many years, between the ants, which want to get into the purple tubes, and the thistle-plants which want to keep them out.
The devices of the thistle to this end are many and wonderful. Beginning at the ground (as the ant does), we find that the stem of the plant is clothed all the way up with fuzz or hairs. This makes things unpleasant for the crawler, for "nothing," says Sir John Lubbock, "bothers ants like hairs." In some varieties of thistle the stem looks as if it had been wound around and around with spider-webs, and often these are gummy, and likely to catch the crawling insect as it tries to work its way up.
Along the stem, here and there, are leaves. These in many varieties have horny edges which roll backward, making a barrier which the ant finds it very difficult to surmount. The under sides of these leaves are often thickly clothed with long, cobwebby hairs, nets to snare the little clam-berer and hold her.
A persevering insect which labors to the top of the stem past the deterrent leaves finds herself before an armed body-guard which surrounds the flowers, a close frill of small leaves, often with recurving margins and thickly set with thorns. And in some kinds of thistle a crawler which has worried through all these obstacles meets and succumbs to a still greater difficulty at last. The many flowers which compose the thistle-head grow all together in a deep-green cup. This cup is made up of overlapping scales, and around it, in many varieties of thistle, more cobweb is wound.
In the common swamp- and pasture-thistles (Fig. 96) each scale of the cup has in its centre a whitish streak, which is very glutinous. Here the luckless crawler comes utterly and finally to grief, after all her struggles and in full view of her goal. She is held fast on the gummy streaks, and her frantic struggles to free herself only result in bogging her more hopelessly. The gum after a while stops up the little holes in her sides through which she breathes, and she is thus smothered to death.
Her fate is not only tragic but perplexing - for here is the higher being sacrificed to the lower, and the more sentient to the less sentient.
Fig. 96. - Pasture-thistles (Cnicus pumilis).
One can scarcely think of a plant so fertile in defensive devices as an insensate thing, and is half inclined to fancy that the thistle continues to practice in modern times those savage modes of warfare once used by the Highland chieftains who carried it on their standards.
Nature is full of problems, and one of the most difficult is to reconcile some of its doings with the Divine Law of love. For we know that "the Lord our God is One" in Nature and in Revelation, and that "if Nature is the garment of God it is woven throughout, without seam"; its loveliness, its terror, its tenderness, its seeming cruelty are all parts of one beneficent and majestic whole. Yet Nature seems to us with our imperfect knowledge a blending of irreconciliable things.
The solution of one question is but the suggestion of another, and the ultimate questions remain wrapped in mystery as deep as that which enfolded them when God spake out of the whirlwind and propounded problems which neither Job nor his friends could solve.
Meantime a wood-thrush close by is asking over and over again that wistful question which the wood thrushes ask each other: a question expressed in a rising cadence, which passes into silence before we can fully enjoy the exquisite timbre of its individual tones.
And after the question has been many times repeated, there comes at last, from far across the sunlit fields, that falling cadence which is the sweet and satisfying answer to it.
Is he prophet as well as poet, this wood-thrush, with his work-a-day brown jacket and spotted vest? After our many questionings will we get our answer too, - altogether satisfying and utterly sweet? The thrush seems appalled at such grave questionings, and flits off to his friends in the tree-tops who have not learned to "look before and after." And as we see the last flicker of his wings we thank him not only for his song, but also for its suggested parable.