The formation of vegetable mould, through the action of worms, with observations on their habits

Abstract

one which has long remained undisturbed for pasture, and where the vegetable mould is exposed on the sides of a ditch or hole.The subject may appear an insignificant one, but we shall see that it possesses some interest; and the maxim " de minimis lex non curat," does not apply to science.Even Elie de Beau- mont, who generally undervalues small agen- cies and their accumulated effects, remarks,* " la couche tres-mince de la terre vegetale est un monument d'une haute antiquite, et, par le fait de sa permanence, un objet digne d'oc- cuper le geologue, et capable de lui fournir des remarques interessantes."Although the superficial layer of vegetable mould as a whole no doubt is of the highest antiquity, yet in regard to its permanence, we shall hereafter see reason to believe that its component particles are in most cases removed at not a very slow rate, and are replaced by others due to the dis- integration of the underlying materials.As I was led to keep in my study during many months worms in pots filled with earth, I became interested in them, and wished to * " Le9ons de Geologie Pratique," tom.i. 1845, p. 140.* " Bidrag till Skandinaviens Oligochsetfauna," 1871.f " Die bis jetzt bekannten Arten aus der Familie der Regenwurmer,' , 1845.io HABITS OF WORMS.Chap.I. will be given in which they had burrowed through the floor of a very damp cellar.I have seen worms in black peat in a boggy field; but they are extremely rare, or quite absent in the drier, brown, fibrous peat, which is so much valued by gardeners.On dry, sandy or gravelly tracks, where heath with some gorse, ferns, coarse grass, moss and lich- ens alone grow, hardly any worms can be found.But in many parts of England, wher- ever a path crosses a heath, its surface becomes covered with a fine short sward.Whether this change of vegetation is due to the taller plants being killed by the occasional trampling of man and animals, or to the soil being occa- sionally manured by the droppings from animals, I do not know.*On such grassy paths worm-castings may often be seen.On a heath in Surrey, which was carefully examined, there * There is even some reason to believe that pressure is actually favourable to the growth of grasses, for Professor Buckman, who made many observations on their growth in the experimental gardens of the Royal Agricultural College, remarks (" Gardeners' Chronicle," 1854, p. 619) : " Another circumstance in the cultivation of grasses in the separate form or small patches, is the impossibility of rolling or treading them firmly, without which no pasture can continue good."HABITS OF WORMS.Chap.I. autumnal rains.Although most coppices and woods support many worms, yet in a forest of tall and ancient beech-trees in Knole Park, where the ground beneath was bare of all vegetation, not a single casting could be found over wide spaces, even during the autumn.Nevertheless, castings were abundant on some grass-covered glades and indentations which penetrated this forest.On the mountains of North Wales and on the Alps, worms, as I have been informed, are in most places rare; and this may perhaps be due to the close proximity of the subjacent rocks, into which worms cannot burrow during the winter so as to es- cape being frozen.Dr. McIntosh, however, found worm-castings at a height of 1500 feet on Schiehallion in Scotland.They are numerous on some hills near Turin at from 2000 to 3000 feet above the sea, and at a great altitude on the Nilgiri Mountains in South India and on the Himalaya.Earth-worms must be considered as terres- /rial animals, though they are still in one sense semi-aquatic, like the other members of the great class of annelids to which they be- Chap.I. NOCTURNAL.13 long.M. Perrier found that their exposure to the dry air of a room for only a single night was fatal to them.On the other hand he kept several large worms alive for nearly four months, completely submerged in water.*During the summer when the ground is dry, they penetrate to a considerable depth and cease to work, as they do during the winter when the ground is frozen.Worms are noc^ turnal in their habits, and at night may be seen crawling about in large numbers, but usually with their tails still inserted in their burrows.By the expansion of this part of their bodies, and with the help of the short, slightly reflexed bristles, with which their bodies are armed, they hold so fast that they can seldom be dragged out of the ground with- out being torn into pieces.f During the day they remain in their burrows, except at the pairing season, when those which inhabit ad-* I shall have occasion often to refer to M. Perrier's admirable memoir, " Organisation des Lombriciens terrestres " in " Ar- chives de Zoolog.exper.,"tom.iii.1874, p. 372.C. F. Morren(" De Lumbrici terrestris," 1829, p. 14) found that worms en- dured immersion for fifteen to twenty days in summer, but that in winter they died when thus treated.f Morren, " De Lumbrici terrestris," &c., 1829, p. 67.