382 



FLORA AND SYLVA, 



of clay that soils too compact are by it made 

 friable and easily worked. It minimises the 

 effect of heatandcold,and combats the hurtful 

 properties of certain mineral substances. It is 

 the principal agency in a natural process of 

 mellowing which, in its results, is best com- 

 parable to that of cultivation. It has recently 

 been shown by a Danish professor, Dr. Miiller, 

 that myriads of organisms exist in forest humus 

 — plant-eaters and flesh-eaters — which pierce 

 galleries and transform it into a living mass of 

 creatures, struggling one against the other for 

 existence. Very soon, in their quest of food, 

 animals of ahigherorder such as shrews, moles, 

 and wild boars, complete the blend of soil, sub- 

 soil, and leaf-mould, as thoroughly as if it had 

 been done with the spade or the plough, and 

 to this mechanical process the trees also con- 

 tribute by their root-action. 



But the question arises, if the leaves return 

 to the soil only what they took from it, how, 

 if at all, is there returned the valuable materials 

 lost at each forest thinning, and which — spite 

 of their comparative unimportance it may be 

 — represent a dead loss to the soil ? This re- 

 newal is brought about by a "mobilisation," 

 if we may so call it, of reserves latent in the 

 soil, by processes which we shall explain. The 

 first question is : Whence comes the deficient 

 nitrogen ? because, even if the phosphates and 

 the potash remain imprisoned in the soil so 

 long as plant life is not there to draw upon 

 them, it is certain that the nitrates are easily 

 drained away with the surface water. It is ad- 



J 



mitted that the nitrous elements dissolved in 

 rain, snow, anddew, during their passage down 

 the roots of great trees furnish to these larger 

 quantitiesof nitrogen than can be the case with 

 agricultural crops which penetrate only a thin 

 layer of soil. Yet even these larger quantities 

 of nitrogen are insufficient to maintain the 

 balance of demand and supply. The result of 

 Professor Henry's research is to show that this 

 deficiency is made up by thecovert, dead leaves 

 having the faculty of absorbing nitrogen from 

 the air as plants of the Pea tribe often do in 

 agriculture. It has been proved that the gain 

 in nitrogen from this source may amount to 

 1 7 lbs. to the acre in the case of Oak leaves, and 

 26 lbs. in the case of Hornbeam. Certain leaves 

 like those of the Beech and Pine, being hard 

 and tough, are very slow to decay, whilst those 



' of the Hornbeam, Elm, and Ash, which when 

 green are eagerly eaten by stock, are as greedily 

 devoured by the plant-eaters in the soil when 

 dry. On the other hand, in the presence of ex- 

 cessive moisture the action of oxygen and of 

 heat is much lessened, and the decomposition 



I of such debris is slow and imperfect. Acid com- 

 binations are also freely produced, resulting in 

 a dry residuum resembling peat, in which only 

 the Alder, Birch, Aspen, and Mountain Pine 

 among thegreaterforesttreesareableto thrive. 

 Inversely, where there is excessive drought the 

 soil becomes parched, crumbling, and fibrous, 

 wearing gradually into a brown or black pow- 

 der which is not at all easily decomposed, and 



j is a veritable dry peat with all its drawbacks. 

 It is chiefly found in sandy soils, where it goes 

 to form what is known as " peat soil." Dr. 

 Miiller tells how to distinguish the various 

 sorts of humus. In leaf-mould, where carbonic 

 acid is the only acid so to speak, animal life 

 abounds and worms are common, it is con- 

 stantly turned by moles and wild boars, and 

 amongthe plantsnativeto itare the Woodruff, 

 the Dog Mercury, the Oxalis, and the Wood 

 Anemone. Peat, on the other hand, is a sort of 

 felt, held together by the tangle of surface roots 

 and by afunguspeculiarto the soil. Sometimes 

 it may be dry and powdery, at others porous 

 as a sponge and as readily absorbent, but it is 

 always rich in organic acids and supports a low 

 vegetation, and Mosses, which, apart from a 

 few forms of Po/ytn'c, are not to be found at all 

 in humus. The fauna of the peat forest, beside 

 being less varied, is marked by the absence of 

 moles and worms, and deprived of theiragency 

 has to depend upon chemical means of decom- 

 position. 



Peat soils prevail in the cold and foggy 

 regions of northern Europe ; further south, 

 where the growing season is longand lime soils 

 abound, it is much less common. Dry peat 



j is, however, often met with in sandy forests, 

 and moist peat upon the mountains. By filling 



! up the gaps in woods, preserving the under- 

 growths, and avoiding too frequent thinning, 

 forest culture aids the formation of dry covert; 

 its removal is so injurious to the wood that it 

 means a loss of 50 percent, or more in output. 

 In soils composed of leaf-mould long rotations 

 are better than short, in order to expose the 

 soil as little as possible ; it is important also 



