There are those who maintain that it is just as practical to develop a dwarf, early variety of corn in the middle latitudes with careful selection as it is to develop a variety of equal earliness when the planting is done in the north.  These maintain that the reason the dwarf, early varieties of corn are not normally developed in the middle latitudes is because the selection in those places is usually made from the large plants which yield well, instead of from the small, early plants, such as would be naturally selected at the north.

By the same reasoning it is held that the constant growing of any species or variety in the northern latitudes does not increase hardiness but only enables us to determine which is hardy, thereby enabling us by selection to increase the hardiness of our varieties.

[Illustration:  Cat-leaf weeping birch and shrubbery on campus of Agricultural College at Fargo, N.D.]

We must admit that this reasoning has a sound scientific basis, its principal weakness at the present time being that there has not been enough experimental work done to determine how general and constant its application is.

However true it may be as a scientific principle, we have on the other hand the undoubted fact that varieties of certain plants, like the cauliflower, are so strongly modified by environment that the varieties disappear altogether as such unless the breeding plants are grown under very definite conditions.  It is well known that cauliflower seed can be grown, for instance, only in certain parts of Europe around the North Sea and to a limited extent in the vicinity of Seattle, and that cauliflower seed from any other region produces plants which not only lose all varietal characteristics but which scarcely resemble cauliflower at all.

As an illustration of this same principle millet affords an excellent example.  Grown at the north for a number of years, without change of seed, it becomes short with stiff straw and very large heads, yielding a large quantity of seed.  When grown as far south as Tennessee for a period of five years only, it assumes a very different character, being tall and leafy with small heads and not very productive of seed.  It might be possible by very rigid selection to develop a variety of millet that would tend to be tall and leafy even in the north, but it is doubtful if it would remain so, and the difficulty of keeping it up to type would be too great to make it profitable.

All this is equivalent to saying that there are certain unstable varieties that are so influenced by climate that it is not good practice to try and keep them up to any given standard except when they are grown in regions which naturally develop the type that we are seeking to maintain.

The more striking examples coming under this class are cauliflower, millet, onions, tobacco and some of the flowering plants.