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It is quite otherwise, however, with the soil and its constituents. Land, we all know–or if we don’t, it isn’t the fault of Mr. George and Mr. A.R. Wallace–land is ‘naturally limited in quantity.’ Every plant therefore struggles for a foothold in the soil far more fiercely and far more tenaciously than it struggles for its share in the free air of heaven. Your plant is a land-grabber of Rob Roy proclivities; it believes in a fair fight and no favour. A sufficient supply of food it almost takes for granted, if only it can once gain a sufficient ground-space. But other plants are competing with it, tooth and nail (if plants may be permitted by courtesy those metaphorical adjuncts), for their share of the soil, like crofters or socialists; every spare inch of earth is permeated and pervaded with matted fibres; and each is striving to withdraw from each the small modicum of moisture, mineral matter, and manure for which all alike are eagerly battling.

Now, what the plant wants from the soil is three things. First and foremost it wants support; like all the rest of us it must have its pou sto, its pied-a-terre, its locus standi. It can’t hang aloft, like Mahomet’s coffin, miraculously suspended on an aerial perch between earth and heaven. Secondly, it wants water, and this it can take in, as a rule, only or mainly by means of the rootlets, though there are some peculiar plants which grow (not parasitically) on the branches of trees, and absorb all the moisture they need by pores on their surface. And thirdly, it wants small quantities of nitrogenous matter–in the simpler language of everyday life called manure–as well as of mineral matter–in the simpler language of everyday life called ashes. It is mainly the first of these three, support, that the farmer thinks of when he calculates crops and acreage; for the second, he depends upon rainfall or irrigation; but the third, manure, he can supply artificially; and as manure makes a great deal of incidental difference to some of his crops, especially corn–which requires abundant phosphates–he is apt to over-estimate vastly its importance from a theoretical point of view.

Besides, look at it in another light. Over large areas together, the conditions of air, climate, and rainfall are practically identical. But soil differs greatly from place to place. Here it’s black; there it’s yellow; here it’s rich loam; there it’s boggy mould or sandy gravel. And some soils are better adapted to growing certain plants than others. Rich lowlands and oolites suit the cereals; red marl produces wonderful grazing grass; bare uplands are best for gorse and heather. Hence everything favours for the practical man the mistaken idea that plants and trees grow mainly out of the soil. His own eyes tell him so; he sees them growing, he sees the visible result undeniable before his face; while the real act of feeding off the carbon in the air is wholly unknown to him, being realizable only by the aid of the microscope, aided by the most delicate and difficult chemical analysis.

Nevertheless French chemists have amply proved by actual experiment that plants can grow and produce excellent results without any aid from the soil at all. You have only to suspend the seeds freely in the air by a string, and supply the rootlets of the sprouting seedlings with a little water, containing in solution small quantities of manure-stuffs, and the plants will grow as well as on their native heath, or even better. Indeed, nature has tried the same experiment on a larger scale in many cases, as with the cliff-side plants that root themselves in the naked clefts of granite rocks; the tropical orchids that fasten lightly on the bark of huge forest trees; and the mosses that spread even over the bare face of hard brick walls, with scarcely a chink or cranny in which to fasten their minute rootlets. The insect-eating plants are also interesting examples in their way of the curious means which nature takes for keeping up the manure supply under trying circumstances. These uncanny things are all denizens of loose, peaty soil, where they can root themselves sufficiently for purposes of foothold and drink, but where the water rapidly washes away all animal matter. Under such conditions the cunning sundews and the ruthless pitcher-plants set deceptive honey traps for unsuspecting insects, which they catch and kill, absorbing and using up the protoplasmic contents of their bodies, by way of manure, to supply their quota of nitrogenous material.