The Need for a Large Stock of a Same Species for Its Preservation

In going northward, or in ascending a mountain, we far often are meet with stunted forms due to the directly injurious action of climate. So it is when we travel northward, but in a somewhat lesser degree, for the number of species of all kinds, and therefore of competitors, decreases northward. On the other hand, in many cases, a large stock of individuals of the same species, relatively to the number of its enemies, is absolutely necessary for its preservation. But anyone who has tried knows how troublesome it is to get seed from a few wheat or other such plants in a garden.