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Adaptation to Soils.
must follow that the promiscuous and wholesale dissemination of a few varieties over the country must eventually cease, and that local and special sorts must constantly tend to drive out the cosmopolitan and general varieties. In this country, it is only in the strawberry that the peculiarities of adaptation of varieties to soils have begun to be well understood; and this is rather because the subject is forced upon the attention by the short generations and constantly shifting plantations of the plant than from any investigational motive.
Many of our fruits are very cosmopolitan as to soils, although there are, probably, none of them which are indifferent to even comparatively minor variations in land. Of the temperate fruits, the apple undoubtedly has the most generalized adaptabilities to soils, and this is closely seconded by the domestic plum. Amongst semi-tropical fruits, the orange thrives upon a wide range of soils. The peach and grape are more exacting, and the same may be said of the pineapple amongst semi-tropical fruits.
Now and then fruits are made to grow in soils which are uncongenial to them by working them upon adaptive stocks. Thus the plum may thrive in sandy regions when it is budded upon the peach, the pear is sometimes grown upon very light lands by working it upon the mountain ash, and the mahaleb cherry is thought by most persons to be a better stock for strong soils than for light ones. We may look for the time when certain varieties of the same species may be selected as stocks for
given soils. But all this forced adaptation to soils is a very special matter, and it only illustrates the more strongly the great importance of giving particular attention to the general subject of the adaptabilities of species, varieties, and even of strains, to variations in soils.
The parasite determinant.-Inasmuch as many of the organisms which seriously interfere with fruitgrowing are more or less restricted in their range, it would seem to follow that the zones of profitable fruit-culture may be determined more or less by the parasite factor. A moment's reflection will show, however, that the geographical distribution of the parasite is determined primarily by climate and by the distribution of its host-plants; so that, on the one hand, the climatal limit of the cultivation of the fruit may be approximately the climatal distribution of the pest, and, on the other hand, the parasite is local or cosmopolitan according as fruit is either local or widely grown.
Many of the common pests are restricted in range because they have not yet reached the full limit of their distribution. An excellent illustration of this fact occurs in the case of the codlin-moth. A generation ago, Michigan was represented to be the Eutopia of the apple-grower because of the absence of this pest, and in our own day similar recommendations have been made of Oregon and other far western states. To the naturalist, however, it was evident from the first that the insect was following closely behind the apple frontier, as a storm follows
The Alarm of Insects and Fungi.
an area of high pressure. It is evident, too, that no amount of legislative enactment could have stayed the dispersion unless it should have forbidden the planting of apple trees.
As a matter of practice, the energetic and intelligent fruit-grower will think last and least of the parasite factor when locating his plantation, for this factor is variable and migratory, and, moreover, there are means of keeping most fruit pests under control. Insects and fungi are apt to be bugbearssometimes literal bugbears-to the fruit-grower; but, after all, they are rarely to be counted upon as permanent factors, and they are the direct and perhaps the most efficient means of keeping the farmer in a state of mental alertness. There are a few cases, of course, to which these remarks will not well apply, but they are clearly exceptions. One of these is the dreaded nematode root-knot of the southern states, and one might seriously hesitate in planting peaches where the ground does not freeze deep enough to destroy the pest. The professional experimenters can determine the course of the lifehistories of the various pests, and can point out their most vulnerable points, and may even devise general means for their eradication; but the final application of this knowledge is a local problem, which each man must work out for himself. Laws are generally of little avail for the destruction of pests, except in those few cases in which disease is more or less permanent or perennial, and in which there is no practicable recourse but to destroy the
plant or the part affected. Such troubles are peach yellows, and black-knot of the plum and cherry. A law cannot be enforced unless public sentiment is behind it, and when public sentiment is aroused the law is not needed. Yet a law is often useful for a time to awaken public sentiment and to call attention to the evil. The final recourse is always greater knowledge and enlightenment.
There are also insurmountable difficulties in the enforcement of laws designed to control the spread of noxious insects and fungi, because it is practically impossible to detect the eggs of insects or of fungi upon a large number of plants, and because there are so many natural and uncontrollable ways in which the parasites may spread. The recent Maryland law, designed to prevent the introduction of fruit-tree diseases and pests, is a case in point. It requires that "whenever any trees, plants or vines are shipped into this state from another state, every package thereof shall be plainly labeled on the outside with the name of the consignor, and a certificate showing that the contents had been inspected by a State or Government officer, and that the trees, plants or vines therein contained are free from all San José scale, yellows, rosette and other injurious insect or disease." It would be impossible for any botanist to certify that a dormant tree were free of all disease; and even in the matter of San José scale, an entomologist could not give a clean bill of health without giving more time to the examination of a tree than it is worth. In the operating of
this law, trees are allowed to pass if an officer certifies that he has examined them and has found no evidence of disease thereon, which is a very different matter from asserting that they are free from disease, and which is a virtual acknowledgment that this clause of the law really cannot be enforced. The best laws of this nature, and for the regulation of spraying and the like, are probably those which are not mandatory, but which provide a protection or a legal remedy in case any person considers himself to be endangered or injured by the perverseness or the negligence of another; and it is a question
if the common law does not provide ample redress for such grievances. There are instances, too, in which it may be wise to make a general effort to stamp out a pest when it first obtains a foothold in America, but this is a very different matter from the endeavor to control the spread of insects and fungi between the different parts of the country. The fact is, that most insects and diseases are beyond the reach of legislative fiats, and it is time that the fact were fully learned. The demand for functionary proceedings against the bugs sometimes recalls the laborious efforts of the Middle Ages. "At one time," writes Fernald,* "a thoroughgoing procedure, according to all the rules of jurisprudence, occurred before the spiritual judge. The accused insects were summoned, and in case of non-appearance, which always occurred, unless the insects were moving to new feed
*C. H. Fernald, "The Evolution of Economic Entomology," Proc. Eighth Annual Meeting Assoc. Econ. Entomologists, 1896.