its service. It surrounds them as a spider its prey, with a fibrous net of narrow meshes, which is gradually converted into an impenetrable covering; but whilst the spider sucks its prey and leaves it dead, the fungus incites the algae found in its net to more rapid activity, nay, to more vigorous increase." This may be all very poetical, but it is not very explicit, and needs a commentary. This we furnished very many years since, and it has never been called in question, but corroborated, to the following effect: that the two great points sought to be established are these, that what we call lichens are compound organisms, not simple, independent vegetable entities; and that this compound organism consists of unicellular algæ, with a fungus parasitic upon them. The coloured gonidia which are found in the substance, or thallus, of lichens, are the supposed algæ, and the cellular structure which surrounds, encloses, and imprisons the gonidia, is the parasitic fungus, which is parasitic on something infinitely smaller than itself, and which is entirely and absolutely isolated from all external influences. In plain words, the gonidia are algæ, and all the rest of the plant is fungus.

This hypothesis has so few adherents, and those few of such little eminence or authority, that it would be quite unnecessary and impolitic to reopen the discussion or repeat the arguments against it, which have never been successfully controverted. mere historical summary, it may be advisable to state a little more definitely what were the points in dispute, and, in doing so, to intimate, as a matter of fact,

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that no lichenologist of any repute, and no mycologist of any authority, supported the theorists during the controversy, but rejected their views as untenable. This is important, as an historical fact, since these were just the scientific men who were practically the best acquainted with the organisms in question, and whose judgment would have the greatest weight. Lichens consist, normally, of a thallus, or vegetative system, which in many species is a tough coriaceous expansion, horizontal or vertical, attached at the base for its support to rocks, stones, wood, and other substances, but not deriving sustenance from the object to which it is attached. In the interior of this thallus minute green bodies, or cellules, form a sub-cortical layer, which are denominated gonidia, and which Dr. Nylander, a most eminent lichenologist, says, "constitute a normal organic system, necessary and of the greatest physiological importance, so that around them we behold the growing (or vegetative) life chiefly promoted and active." In addition to these is the reproductive system, which consists of apothecia, or discs, borne upon the thallus, containing the asci and sporidia, or reproductive organs. Such are the organisms which have been called lichens, and are regarded by the best scientific authorities as complete and autonomous plants, equally with fungi and algæ, amongst the lower cryptogamia. On the other hand, the theorists contended that the thallus and reproductive system were, not only fungoid in character, but absolute fungi, whilst the green gonidic layer of cellules were simply unicellular algæ, upon which the fungus was parasitic. Hence the lichens

were not autonomous plants, but mere compounds of fungus and algæ.

This contention was opposed on the following grounds: and, firstly, that the so-called fungoid element was not a fungus, because lichens are perennial; they grow very slowly, but they attain an extreme age. Some species, growing on primitive rocks of the highest mountains in the world, are estimated to have attained an age of at least a thousand years; and one author mentions, after the lapse of half a century, having observed the same specimen of Sticta on the same spot of the same tree. On the other hand, fungi are mostly annual, very short-lived, their whole existence being limited to a few weeks, rapid in growth, and rapid in decay, not a trace of some species remaining after a few days.

Lichens will exist under conditions of aridity which no other vegetables could support. Some are peculiar to calcareous rocks, a few on arenaceous rocks, many are common on the granitoid series, and one, Lecidea, is frequent on the purest and smoothest quartz. Fungi, on the contrary, must have moisture for their very existence' sake, are mostly found in damp and shaded situations, and could never exist under the conditions above enumerated for lichens. Of all plants lichens support extreme cold most successfully, whilst fungi succumb at the approach of frost.

Lichens which grow upon the bark of trees may be seen flourishing in profusion during the life and vigour of the tree. Cinchona bark which has been covered with lichens during growth has its qualities improved, whereas the portions attacked by fungi

are valueless from the tissue being destroyed by the mycelium. Fungi do not, and cannot, flourish on growing and vigorous bark, but on diseased, dead, or decaying spots.

Lichens obtain the greater portion of their pabulum from the atmosphere, and only their mineral constituents from the matrix. Fungi obtain their chief support from the decaying vegetable matter on which they flourish, gathering up the nitrogenous results of decay, and disintegrating the matrix on which they prey. Lichens are preservers, whilst fungi are destroyers.

Lichens, in their chemical composition, contain a large number of substances which are wholly unknown amongst fungi. Likewise they hold but a small percentage of water, as compared with fungi, so that in dessication they do not shrivel, collapse, or diminish perceptibly in size; whereas fungi shrivel, and collapse, and are constantly liable to the attacks of insects, or, if damp, to the development of mould. Lichens may be preserved for years without fear of insect or mould.

The contention' was also opposed on the ground that the gonidia are a part of the lichen structure, and are consequently not appropriated green algæ. Lichenologists, with one consent, admit them as essential parts of lichen structure. One says that they may be regarded as intermediate in function. between the vegetative and reproductive cell, assuming the offices, and partaking of the characters of both. Nylander contends that the absurdity of the hypothesis is evident from the very consideration that it

cannot be the case that an organ (gonidia) should at the same time be a parasite on the body of which it exercises vital functions. If the gonidia are true algæ, it was contended by the opponents of the hypothesis, it is insufficient to state that they so closely resemble alge that they might be mistaken for such; there must be some undoubted evidence produced that they are algæ in fact, and not in appearance. It has been demonstrated that the gonidia are developed within the substance of the lichen itself, in a determinate and uniform manner; that, instead of being altogether a foreign substance, they are generated within it, and hence, according to the theory, the parasite produces from its own substance the host upon which it is parasitic, which is an absurdity. "Parasitic existence is autonomous, living upon a foreign body, of which nature prohibits it from being at the same time an organ."

From the foregoing and similar facts, it was concluded that the assumption that two separate and distinct organisms are combined in one plant, which by its own proper system of reproduction is capable of continuing the species, each individual of its progeny also exhibiting the same phenomena of dual existence, is inconsistent with known scientific facts, because whilst one supposed plant proceeds from its proper germ, the other has none, and is, therefore, spontaneously evolved.

The theory assumes further, that a fungus is parasitic upon a smaller and weaker organism, which it does not injure or destroy. This again is contrary to scientific fact, as it confers upon, or assumes for a destructive force conservative powers,