Page:Popular Science Monthly Volume 43.djvu/232

220 columbine is particularly well adapted for having its seeds scattered by the wind. They are held in open seed vessels surmounting a slender stalk which, although nodding at flowering time, has become upright. A slight breeze easily shakes this stalk, causing the seeds to be thrown for quite a distance. The poppy throws its seeds in a similar way, and the little eaves which stand over the holes in the pod are even said to close in wet weather, not allowing the seeds to escape.

In many wonderful instances the ripe pod projects its seeds forcibly into the air. In some of our wild violets the pod, after dehiscence, consists of three spreading valves, each shaped like a boat, bearing within several seeds which are pear-shaped, hard, and smooth. In drying, the valve walls contract, approach each other, and squeeze out the seeds, which are thus thrown several feet. Our wild witch-hazel throws its seeds often to the distance of thirty feet. Many of us recollect the sudden bursting and coiling up of the pods of the "touch-me-not," whose yellowish, spurred flowers are so common in moist places. The object of this action is to expel the seeds. Curious is the case of the squirting cucumber of southern Europe. The ripe, cucumber-like fruit is greatly distended by its contents. At a slight touch, as from a browsing animal, it breaks from the stalk, and through the hole thus formed the pressure of the elastic walls forces the seeds in a viscid liquid for twenty or thirty feet.

Fruits that do not split open are invariably scattered by external means, inanimate and animate. Of inanimate agencies the wind is far oftenest employed, and seeds have evidently found it extremely efficient, judging from their many adaptations for wind dispersion. The seeds of our elms, maples, pines, etc., are surrounded, as we know, by thin expansions called "wings," whose purpose plainly is to present a large surface for the wind to act upon. Wings are characteristic alone of trees or tall shrubs, and never occur on low herbs, where they would clearly be out of place. Instead of a wing, a tuft of hairs frequently serves the same purpose. A common example is furnished by the milkweed, whose seed is surrounded by a spreading "pappus" of long, silky hairs. The dandelions and thistles have adopted this means of distribution, and this explains their abundance everywhere. In the smoke-bush of our gardens only a few flower stalks bear fruit, the rest become slender and feathery, forming a light network which is borne along in the wind, carrying the few small fruits which have formed.

Flowing water transports many large nuts, some depending upon it almost exclusively. Drifting along in our fresh-water streams one may often see the "key fruits" of the red maple, and the soaking they thus receive must further germination. The