IN addition to their spore-bearing spots, lichens have for some time been known to possess other organs, termed spermogones, which are probably concerned more or less in the reproductive process. The first intimation of the existence of similar bodies in the entophytal fungi originated with M. Unger in 1833, but it was left to Dr. de Bary and the Messrs. Tulasne, twenty years later, to examine and determine satisfactorily the nature and value of the spermogones of the Uredines. It was at first believed that the smaller pustules—which sometimes precede, and sometimes accompany, the cluster-cups and some other allied fungi—were distinct species developed simultaneously therewith, or members of a new genus, which, under the name of Æcidiolum exanthematum, found a place in the mycologic system.

Without staying to trace the stages through which the elucidation of their true nature proceeded, it will suffice for our purpose to tell what is now known of these secondary organs; to accomplish which we must stand greatly indebted to the independent researches of Messrs. de Bary and Tulasne. It has been demonstrated that both these bodies, namely, the primary organs or cluster-cups, and the secondary organs or spermogones, are developed from the same mycelium; but the value of the latter is still undetermined. If they possess any fecundative power, the process has not been traced; or if they are in themselves reproductive, they have not at present been seen to germinate. Their uses, therefore, in the economy of the parasitic plant of which they are now known to form a part is still a mystery, and they remain valueless in the determination of genera and species. Any speculation which might regard them as male organs would be premature, and without support in fact. Hitherto only some species of the genera described in the foregoing chapter, and others belonging to genera not hitherto named, have been ascertained to possess spermogones. Of the former are the RoesteliÆ, some species of Æcidium, as those of Euphorbia, &c., and Peridermium Pini.

These spermogones are of a very simple structure—very delicate, indeed; so much so, that they will scarcely bear preparation for demonstration. De Bary states that they originate from plain, delicate, inarticulate threads, about half the thickness of the mycelium (the root-like branching fibres which form the fundamental stratum of fungoid growths), which are developed in large quantities, and closely packed together. These threads are compacted together so as to form an outer enveloping integument or peridium, which is either globular or hemispherical (or in some instances elongated), more or less immersed, and at length opening at the apex (fig. 153) by a regularly formed minute ostiolum. The inner wall of the peridium is covered with a thick forest of simple filaments standing on end. From the summit of these filaments or sterigmata, the spermatia are borne. These are either isolated or associated together in strings or chaplets, are exceedingly minute, of an ovoid or oblong shape, and are produced in such numbers as to fill the cavity of the spermogone. Besides these, a viscid fluid is secreted, in which the spermatia are immersed, and which is expelled with them from the orifice of the peridium. According to the density of this fluid, or the hygrometric state of the atmosphere, it appears sometimes in drops, and sometimes oozing out in threads or cirrhi from the spermogones. To compare minute things with gigantic, as a recent author has observed, it resembles the lava issuing from the crater of a volcano. The colour of this spermatiferous matter is commonly orange, but in some instances brown, though not constantly of the same colour as the spores produced from the same mycelium. This gelatinous substance is dissolved away from the granular bodies which are immersed in it, by adding a little water upon the slide on which the mass is placed for examination. The granules, or spermatia, then exhibit those peculiar movements which have been observed in the similar bodies in lichens, and fitly described as “a sort of oscillating motion, as of a body attached at one extremity.” The cause of this motion is at present uncertain, vibratile ciliÆ, to which similar movements are referred, being altogether absent; but probably, as De Bary believes, the cause may be found in the influence of exosmose.

The largest spermatia yet examined (those of Peridermium Pini) have a length equal to 1/2500 of an inch, but their width seldom exceeds 1/100000 of an inch, whilst in others their length does not exceed the width of those just named.

Messrs. Tulasne affirm that all these corpuscles, as well as the mucilaginous fluid, evolve an appreciable odour, resembling that of the pollen of the willow. M. LÉveillÉ compares the odour to that of orange flowers, and M. de Bary to that of the evening primrose.

The spermogones do not always appear like pustules on the surface of the leaves, for sometimes their presence is only indicated by minute depressed punctures which are scarcely visible; generally, however, they may be recognized by an obtuse, or otherwise a pointed, protuberance that surmounts them. The margin of the orifice is sometimes furnished with short hairs, but is more frequently ornamented with a pencil of long hairs, which are stiff and erect, and of the colour of the enclosed spermatia.

In many of the species of Æcidium the cups are disposed in a more or less regular circle, the centre of which is occupied by a group of spermogones; at the same time, the corresponding spot on the opposite surface of the leaf will frequently be found also occupied by other spermogones—in some instances in greater number than on the same surface of the leaf on which the cups are seated. This is the case in the Æcidium which is found upon the leaves of the coltsfoot, and that of the honeysuckle.

Very bright orange-coloured spots may be observed in autumn (we have encountered them often in August and September) upon the leaves of pear trees, and which are covered with little tubercles, at first of the same colour, but ultimately becoming brown. These pustules are so many spermogones belonging to Roestelia cancellata, a kind of cluster-cup found in the same localities. These spots have long since been noticed, and regarded as connected with the Roestelia, but in what manner has until recently been unknown. The Rev. M. J. Berkeley noticed them in the English Flora in 1836, or at least the granulations on the upper surfaces of the leaves bearing R. cancellata, R. cornuta, and R. lacerata, and called them abortive pseudoperidia. Before this (in 1804) they had been observed by Rebentisch. An examination of one of these spots under a low power of the microscope, and afterwards a section of one or more of the pustules, cut with a sharp razor, and viewed with a higher power, will give an idea of the nature of the bodies we are attempting to describe. During the past summer we have noticed very similar orange spots on leaves of the berberry containing spermogones on both surfaces, and these appeared before any cups had been found on that plant. In this instance no cups were produced from the spots on the leaves examined, and which were carefully noticed at intervals until they withered and fell.

In some instances, as in Roestelia cornuta, which is found on the leaves of the mountain-ash, the cups are produced on the lower, but the spermogones almost exclusively on the upper surface.

The spermogones of Peridermium Pini are white, few in number, and are developed, not only in the spring, but sometimes reappear in the autumn upon the same leaves that produced them at the commencement of the year.

In such instances as those of the Æcidium of the spurge, and also the goatsbeard, in which the cluster-cups are arranged in no appreciable order, the spermogones are scattered amongst them, and even in some instances appear on different leaves. The spermogones are common on the wood spurge in spring, scattered over both surfaces of the leaves before the cluster-cups make their appearance, and gradually these latter are developed amongst them, commencing from the apex of the leaves and proceeding in the order of their development towards the base. In this instance the spermogones are bright yellow, as are afterwards the cups and spores of the Æcidium. In most instances the appearance of the spermogones precedes that of the sporiferous organs, but the latter follow sufficiently speedy for perfect development before the decadence of the spermogones takes place.

After the expulsion of the spermatia and the fluid which accompanies them, the whole mass dries up; and where many spermogones have been clustered together in the same spot a brown homogeneous crust is formed upon the epidermis; where they are produced singly, a brownish incrustation is visible about the mouth of each spermogone.

Re-agents applied to the spermogones whilst in full vitality indicate the presence of a considerable amount of a protein substance, which, with sugar and sulphuric acid, produces a deep purple red colour.

From what we have already stated of the method of occurrence of these organs, the following is the only order, apparently, preserved in their development, although no definite rules can at present be affirmed. The spore spots of cluster-cups are generally found upon the under surfaces of the leaves on which they are produced, and the spermogones are most numerous on the upper. When both the cluster-cups and the spermogones appear in the same group on the same surface, the spermogones commonly occupy the centre, and the cups are arranged in a circular manner about them. In other, and fewer instances, both organs stand together indiscriminately upon the same surface.

The spermogones are also developed centrifugally, at least so far as at present observed, for when they are produced in a cluster the central one first opens and discharges its contents, and thus the development proceeds outwards from the centre to the circumference. When the spermogones are scattered, as in those of Euphorbia, they are first observed at the apex of the leaf, whence they are developed in succession towards the base. The latter should be sought for on the young plants of the wood spurge in March or April, at which time we have found them abundant at Darenth wood, near Dartford.

It must not be concluded, from the fact that we have not yet adverted to spermogones in connection with other fungi, that they are peculiar to the Æcidiacei. Such is by no means the case. As we have hereafter described other genera and species in which spermogones occur, it would be out of place to enter upon further details here. Let it suffice therefore that we state that they have been found in members of the genera, Aregma, Triphragmium, Puccinia, Lecythea, Trichobasis, and Uredo, but they have been found much more generally in Roestelia and Æcidium than in any other genus.

As comparatively little is yet known of these bodies, a fair field is open to the enterprising microscopist, with time at his disposal, and a good store of perseverance, to win for himself renown in the discovery of fresh facts, and the elucidation of some of the mysteries which yet enshroud these interesting organisms. From the foregoing pages he will learn the direction in which his researches should tend, and he may be assured that every new fact is of importance when carefully ascertained.