Page:Popular Science Monthly Volume 3.djvu/86

 of an Alexander; and the results of the wars of the plants are assuredly of no less importance, seeing that the very existence of an Alexander depends in no slight degree upon them. The campaigns we speak of are real; they are not mental figments, or allegorical illustrations. Success in the practice of horticulture, of agriculture, of forestry, depends on the action we men take toward the combatants. If we remain neutral, the weakest goes to the wall, overpowered by the stronger; if we interfere, we exert a very powerful influence for the time; but, immediately we cease to exert our power, the combat begins again, and with enhanced violence. The essence of successful cultivation often consists almost entirely in the removal of the plant from the influence of that hostile "environment" to which, under natural circumstances, it would be subjected. It is this that accounts, in a great measure, though of course not wholly, for the oft-observed fact that certain plants, flowers, and fruits, attain far greater perfection in our gardens than they ever do in their native countries.

That a war of extermination is thus going on around us may strike some with surprise. They are so accustomed to associate flowers and plants with peace and repose, that they are astonished to find that other far less amiable ideas may, with even more justice, be associated with them. And yet a moment's reflection, or a passing glance at the nearest hedge-row or pasture, will show the reality of the struggle. All that beautiful disorder, that apparently careless admixture of divers forms and colors—the sweeping curves of the brambles, the entwining coils of the honeysuckle, the creeping interlacement of the ground-ivy or the pennywort—all are but indications of the fray that is constantly going on. It would seem as if the weakest must succumb, must be overpowered by the stronger-growing plants, and so they are at certain places and at certain times; but, under other conditions, the victory may be with the apparently weaker side, just as the slow-going tortoise may outrun the fleeter hare. In any case, the success is often only temporary; the victor becomes in time the vanquished; the vanquished, in its turn, regains its former conquest; and so on.

It is proposed in the following notes to give a few illustrations of the nature and effects of this conflict, of the way in which it is carried on, and of the circumstances which favor it.

Agriculturists had long been practically conversant with the advantages derivable from the practice of not growing the same crop on the same soil for too long a period. The advantages consequent on this so-called rotation of crops are due to more than one cause; but it was Dureau de la Malle who, in 1825, called attention to the phenomenon of natural rotation. From long observation of what takes place in woods and pasture-lands, he established the fact that an alternation of growth, as he called it, occurs as a natural phenomenon. In pasture-lands, for instance, the grasses get the upper hand at one time, the