silk scar? What is the silk? Sketch the grain from the two points of view that show it best. Where is the embryo? Does the grain have endosperm? What is dent corn? Flint corn? How many kinds of corn do you know? For what are they used? [Illustration: FIG. 248.—PECAN FRUIT.] NOTE TO TEACHER.—There are few more interesting subjects to beginning pupils than fruits,—the pods of many kinds, forms, and colours, the berries, and nuts. This interest may well be utilized to make the teaching alive. All common edible fruits of orchard and vegetable garden should be brought into this discussion. Of dry fruits, as pods, burs, nuts, collections may be made for the school museum. Fully mature fruits are best for study, particularly if it is desired to see dehiscence. For comparison, pistils and partially grown fruits should be had at the same time. If the fruits are not ripe enough to dehisce, they may be placed in the sun to dry. In the school it is well to have a collection of fruits for study. The specimens may be kept in glass jars. _Always note exterior of fruit and its parts; interior of fruit with arrangement and attachment of contents._ CHAPTER XXII DISPERSAL OF SEEDS It is to the plant’s advantage to have its seeds distributed as widely as possible. _It has a better chance of surviving in the struggle for existence._ It gets away from competition. Many seeds and fruits are of such character as to increase their chances of wide dispersal. The commonest means of dissemination may be classed under four heads: _explosive fruits_; _transportation by wind_; _transportation by birds_; _burs_. [Illustration: FIG. 249.—EXPLOSION OF THE BALSAM POD.] [Illustration: FIG. 250.—EXPLOSIVE FRUITS OF OXALIS. An exploding pod is shown at _c_. The dehiscence is shown at _b_. The structure of the pod is seen at _a_.] =Explosive Fruits.=—_Some pods open with explosive force and discharge the seeds._ Even beans and everlasting peas do this. More marked examples are the locust, witch hazel, garden balsam (Fig. 249), wild jewel-weed or impatiens (touch-me-not), violet, crane’s-bill or wild geranium, bull nettle, morning-glory, and the oxalis (Fig. 250). The oxalis is common in several species in the wild and in cultivation. One of them is known as wood sorrel. Figure 250 shows the common yellow oxalis. The pod opens loculicidally. The elastic tissue suddenly contracts when dehiscence takes place, and the seeds are thrown violently. The squirting cucumber is easily grown in a garden (procure seeds of seedsmen), and the fruits discharge the seeds with great force, throwing them many feet.