One of the commonest types of dry fruit is the capsule ([Figure 53]), well named, as it is almost an exact counterpart of the capsule of the druggist, in that it is in many cases composed of a lower part and an upper, usually merely a domed lid. Others again, instead of splitting around the sides, split from top to bottom. Still others, as peas and beans, known as legumes ([Figure 57]), are pods that not only split lengthwise, but have no central partition, as do many other fruits of the same general type. When the seed is ripe nearly all pods and legumes finally split open, and the seed or seeds tumble out. A few, as in the violet and touch-me-not or jewelweed, apparently realizing that merely to spill out ripe seeds at the proper time will not spread the species very far, open their fruits with a sudden explosion and literally shoot their seeds considerable distances. The artillery plant, commonly grown in greenhouses, a delicate feathery herb from tropical America, opens its flowers with a report like a toy popgun and shoots its small pollen grains for several feet, but not its seeds as stated by some.
But many fruits do not open at all and seem to be at the greatest disadvantage in the effort to insure
Fig. 52. The strawberry. The fleshy part consists of the modified upper end of the flower stalk or receptacle, while the true fruits are the dry achenes on or embedded in the surface and popularly called the seeds. Fig. 53. A three-celled capsule splitting lengthwise as in the common Iris. Fig. 54. Fruit of the cocklebur, the hooked prickles of which are admirably adapted for clinging to the fur of animals. Fig. 55. Pods of a plant of the Mustard family, which split down both edges, unlike the true peas, which split down only one edge. Fig. 56. Two types of achenes of the daisy family tipped with plumed bristles, greatly aiding their carriage by the wind. Fig. 57. Common garden pea—a typical legume. Note that it splits only on one side. Fig. 58. The samara or two-winged fruit of the maple. Fig. 59. The samara or single-winged fruit of the ash. Fig. 60. The dry two-pronged and bristly fruit of the unicorn plant (Martynia), admirably adapted for dispersal by animals.
dispersal of their seeds. Greater food value to birds and animals overcomes this in some kinds, and another help is that some fruits of this sort are covered with hooked prickles or barbs (Figures [54] and [60]). The common weedy burdock, the barbed fruits of which may often be found sticking to the fur of animals in great quantities, is a case in point. There are whole groups of plants that rely on this method for seed dispersal, notably the avens, tick-seed, tick trefoil, and many shrubs in the tropical regions.