How the Worms Help Us.

Otago Witness, Issue 1650, 7 July 1883, Page 28

How the Worms Help Us.

Mr Darwin's interesting researches respecting the common earthworm, and the recognition of the important influence which this humble annelid exerts in the formation of mould and promoting the fertility of the soil, has led other observers into this field, who have supplemented Mr Darwin's notes with important addenda. Professor V. Hensen has lately Bhown"that the great depth to which some plants send their roots is greatly facilitated if not dapendent upon the channels opened by the large earthworm, Lunibricus terrestris. The smaller species of worm, L. communis, lives and burrows in the superficial soil, whilst the first-named species works principally in the subsoil, its burrows descending to a vertical depth of from three to six feet, and frequently extend further in a horizontal direction. These worm-tubes are lined with a slimy substance, and are studded with little black protuberances formed from the excrement of the animal. It had long been known that some plants, as red clover for example, sent down their roots into the subsoil for two yards or more. The roots of these plants have been observed to follow the tracks of the earthworm, covering the sides of the passages with a thick network of capillaries that feed on the rich mould by which these passages are lined. Professor Hensen says that this can be best studied with plants of the cabbage kind. From analysis this naturalist concludes that worms eat soil simply to make their tubes, and that their real nutriment consists of vegetable matter in process of decay, and, incidentally, a certain proportion of animal matter. The popular prejudice against worms as destructive of growing vegetation by eating their roots has been exploded, as it has been Blea^ly°ip¥oVed',that they only eat what is already dead ' or dying, though the wireworm and various other larvss undoubtedly do so. can be no doubt that the fertility of the soil is greatly promoted by the habits of this qr mature in gathering up stray leayes, &c, and dragging them beneath the soil to rot, and the intimate blending of such vegetable substances Tf^th ttje soil in passing through the alimentary panal of the' wo,rm, being thrown off again in the form of manure and distributed through th,e Bojito depths beyond the ordinary propesaes of agriculture. When we consider that the necessary constituents may be present in the soil, but not in a form that can be assimilated by vegetable growth, or such materials ;nay not be nutrient through the absence of air, carbonic acid, and water, in consequence of its compact character, there is weight in .Professor Henaen's xemark that " chemical Analysis of a subsoil gives no sufficient insight into its fertility if the number of wormholes are not also taken into consideration." The Panish JJoologist, Professor P. E. Muller, has also carried on some interesting observations -bearing on this subject. During the severe winter of 1879-80 he was led to examine the layer of soil immediately below the frozen surface, and as the result of his investigations has demonstrated the existence of " underground dew." After the frost had continued unabated for several weeks the frozen ground was broken through, when 'a moist subsoil was found underlying it ranging from one to two feet in thickness, whilst below this moist Stratum the ground was dryer. This naturalist thinks that the presence of moisture in this way can only be accounted for by the watery vapours rising from the warmer earth beneath being condensed as they approach the frozen surface. The roots of plants running down through the worm tracks would, of course, enjoy a moiat atmosphere by this means, and Professor Muller actually found such roots Beaded with little drops of water. Any additions to our knowledge of the conditions under which. useful plants are best able to thrive is a substantial gain, and the value of the abused earthworm m reference to agriculture is now so far recognised that it is even proposed to introduce them into localities where their numtars ar« deficient.