nature of the soil; thus the couch-grass was ultimately spread over all the plots, whether of sand, or of loam, or of lime, whether drained or undrained. So also with Poa pratensis and Potentilla reptans. So that the chemical and physical nature of the soil, as has been so often shown in similar investigations, plays only a secondary part.
As to the action of shade, it was found by Prof. Hoffmann that low-growing plants, especially if annuals, disappeared rapidly, while taller-growing plants, such as couch, Prunus Paclus, etc., survived. The survival of certain plants, then—couch, Aster, Potentilla, etc.—is due much less to external conditions than to the "habit" of the plant itself; that is to say, to the facility the plant has of adapting itself to varying external conditions, and thus of triumphing over others less favorably endowed in this wise.
The immediate source of victory lies in the powerful root-growth of the survivors, including under the general term "root" not only the root proper, but the offshoots and runners which are given off just below, or on the surface of the ground. Indeed, the latter habit of growth is more advantageous to plants in such a struggle than the development of the true root downward would be. Among those plants where the roots were equally developed there were, nevertheless, inequalities of growth, dependent, probably, on the greater need for light in some species than in others, etc.
It is clear from Prof. Hoffmann's experiments that, but for the continual use of the hoe, and the diligent extirpation of the weeds in our fields, the stronger-growing ones would not only destroy our crops, but also other weeds less vigorous than themselves. But they are not sufficient to explain all the conditions of this complicated problem; as is shown by the fact that, in the district adjoining the locality where Prof. Hoffmann's experiments were carried on, the predominant plants are not the same as those which ultimately proved victors in the experimental beds.
We may add that for two years a series of observations was carried on in the gardens of the Royal Horticultural Society, at Chiswick, with a view to ascertain how certain selected plants, twelve in number, and naturally growing in pastures, would be affected when growing by themselves, by the addition of manures of five, different descriptions, and similar to those used at Rothamsted. In some cases the results of these experiments were unsatisfactory, from circumstances that need not be detailed here; still a large body of facts was accumulated, and, with reference to the property by which certain plants prove victorious in the struggle for life, it was clear that the natural habit or organization of the plant was, cœteris paribus, the mainspring of its success over its competitors. The several manures intensified or deteriorated this peculiar organization, as the case might be, and thus favored or impeded its growth accordingly.—Popular Science Review.
