In hundreds of plants the ripened pods, instead of being erect as their flowers have been, are pointed downward about the time the seeds are ready to be released, and their harvest is sown, sometimes by deliberate movements, in the immediate vicinity. No great areas are captured by such plants, except by the slow process of successive generations extending their range a few inches or at most a few feet a year. The great bulk of all seeds never do grow into new plants, but in those that only shed their seeds close to the parent plant the opportunity to reach new sites is by that much restricted. The chance of the species getting very far afield except by slow invasion of the neighboring region is limited. A few of such plants show remarkable ingenuity in reaching the utmost distance possible, perhaps the most effective cases being those that shoot their seeds by explosive bursting of their pods. Nearly all the violets do this, often shooting seeds several feet from the parent plant. Many plants of the pea family have pods that are twisted, which upon splitting release the previously pinched seeds so suddenly that they are shot considerable distances. In the common witch-hazel (Figure 111), the seed is shot through the air often as much as thirty feet. [Illustration: FIG. 111.--THE WITCH-HAZEL (_Hamamelis virginiana_) Is a fall or winter flowering plant which shoots its seed sometimes as much as thirty feet. Native of eastern North America.] But with even the greatest ingenuity and the most explosive bursting of pods, most plants could never capture much new ground, and their very existence as a species is often contingent on their ability to spread, if these various methods by which plants shed their seeds were not aided by outside help. Some of these have had conspicuous and almost startling results. 1. DISPERSAL BY ANIMALS, THE WIND, AND WATER The seeds or fruits of those plants that are used for animal food are often carried considerable distances, while the thrifty squirrels’ burying of acorns is everyday knowledge to those who have seen them busily engaged in the making of winter stores, or the planting of new trees, often many rods from the parent tree. In years of plentiful seed production squirrels have been known to plant great quantities of seeds of the Douglas fir, thereby hastening the establishment of one of the greatest evergreen forests in the west.