29. Seeds kept dry by an umbrella growing over them.—When mature, the apple of Peru, Nicandra, keeps every dry bursting fruit covered with a hood, umbrella, or shed, so that seeds may be kept continually dry and may be spread with every shake by the wind, or by an animal, in rainy weather as well as in dry.

In the words of Dr. Gray, "The fruit is a globular dry berry, enclosed by a five-parted, bladdery inflated calyx." The margins of the lobes of the calyx curl upwards and outwards as the berry hangs with the apex downward.

FIG. 36.—Mature fruit of apple of Peru covered by an enlarged calyx. FIG. 37.—The same with the calyx removed. FIG. 38.—The same as Fig. 37, except that it is older and somewhat changed.

The berry is as large as one's thumb, and when ripe, bursts open irregularly on the upper side as it hangs up under the calyx. As the covering of the pod opens more and more, a few seeds at a time may be rattled out by wind or animal. The numerous large and light fruits, with calyx surrounding them, are each supported on a nodding stem, stiff and elastic, which gives the wind a good chance to sway them about. Water does not seem to get into the berries even when they are torn open, for when it is poured over the branches it rolls off the calyx roof as freely as from a duck's back. The fruits of Physalis are apparently kept dry in a manner similar to the apple of Peru, although when first mature they are soft and juicy, considerably like a ripe tomato.

30. Shot off by wind or animal.—The calyx of sage, bergamot, and most other mints, remains dry and stiff, as a cup to hold one to four little round nutlets as they ripen. The figure shows two of these in section, as they are attached to the main stem of the plant, or one of its branches. Observe the direction taken by the upper and by the lower points of the calyx. When dry, the plant behaves somewhat as follows: when the wind jostles the branches against each other, or when an animal of some kind hits the plant, this movement causes many of these cups to get caught; but the elastic stem comes suddenly back to its place, and in so doing flips a nutlet or more from its mouth one to six feet, somewhat as a boy would flip a pea with a pea-shooter. In our garden, July 2, when plants of sage, Salvia interrupta, were ripening their fruit, we found it difficult to collect any seeds, but seedlings were observed in abundance on every side of the plant, some to the distance of six feet. Plants dispersing seeds in this manner have been called catapult fruits. Examine ripening fruits of blue curls, pennyroyal, germander, balm, horehound, dittany, hyssop, basil, marjoram, thyme, savory, catmint, skullcap, self-heal, dragon's head, motherwort, and various dry fruits of several chickweeds.

FIG. 39.—Ripe calyx of sage, first as pushed down; second as let loose throwing nutlets.

31. Seed-like fruits moved about by twisting awns.—Most of the grains of grasses are invested with glumes, or chaff, and a considerable per cent of the chaff has awns, some of which are well developed and some poorly developed. The distribution of such grasses depends on several agents—wind, water, and animals. The chaff and awns of all are hygroscopic; that is, are changed by differences caused by variation of moisture in the air. Sweet vernal grass, tall oat grass, holy grass, redtop, animated or wild oats, blue-joint, and porcupine grass are among them. When mature, the grain and glumes drop off, or are pushed off, and go to the ground. When moist, these awns untwist and straighten out, but when dry they coil up again; with each change they seem to crawl about on the ground and work down to low places or get into all sorts of cracks and crevices, where the first rain is likely to cover them more or less with earth, after which they are ready for growth.