Page:Popular Science Monthly Volume 3.djvu/92

 ; from some plots the clovers and umbellifers are banished altogether, while in other cases they may be proportionately increased. Even among the grasses the competition is very severe, and the result in some cases is that all or nearly all have to give way to the cock's-foot grass (Dactylu cœspitosa), the growth of which is so fostered by certain manures as to cause it to overcome its fellows and remain master of the situation. To the plots to which a mixed mineral manure, consisting of salts of potash, soda, magnesia, and lime, is applied, but little difference in the number of species is observable. On the other hand, manures containing ammonia salts, or nitrates, cause a great diminution in the number of species living in the plot to which they are applied. While the unmanured plots furnish by weight about 60 per cent, of grasses, the remainder, consisting of plants of other families, the plots to which admixture of mineral and nitrogenous manures is added, contain as much as 95 per cent, of grasses, and these belonging to a comparatively very few species. Salts of potash and lime, which are comparatively inert as regards grasses, manifest their influence in increasing the vigor and the absolute numerical proportion of the leguminous plants.

The manner in which these results have been arrived at is worthy of a short description in this place.

Notes are taken at frequent intervals during the season of growth, the appearance of the plants noted, their relative luxuriance observed, and their comparative tendency to produce flower or stem and leaf, the abundance of flowers, etc., etc. Root-growth is studied, and also the character of the soil in the various plots, and the way in which its texture and its capacity for holding or transmitting water are modified according to the manure applied. When the crop is cut from each plot, its weight is estimated, and also the amount of dry produce. In some cases chemical analysis is pushed further, and the ashes duly examined. In addition to these no trifling observations, three "separations" have been carried out at regular intervals. These separations consist in the picking out, from a sample of a certain weight taken from each plot, every fragment of every species contained in the sample. In this way the relative quantity and weight of each of the different plants in the several samples are accurately determined, and the proportion in the whole plot computed. The labor is enormous; but the results, when fully brought out, must be most important, both as regards the scientific aspect of the question, the history of the life-struggle between plants so circumstanced, and also as regards the practical hints to be derived by the cultivator.

Some experiments of a somewhat similar character, and bearing directly on the struggle for life among plants, have been made by Prof. Hoffmann, of Giessen, and they are of such interest that we introduce here a very condensed account of them, taken from the pages of the Gardener's Chronicle, 1870, p. 664.