Part 17

See "Corda Icones," tab. 2.

Corda, "Icones Fungorum," vol. vi. Prague.

Tulasne, "Fungi Hypogæi." Paris.

Winter, "Die Deutschen Sordarien" (1873).

Corda, "Icones Fungorum," 6 vols. (1837-1842); Sturm, "Deutschlands Flora," Pilze (1841); Tulasne, "Selecta Fungorum Carpologia;" Bischoff, "Kryptogamenkunde" (1860); Corda, "Anleitung zum Studium der Mykologie" (1842); Fresenius, "Beiträge zur Mykologie" (1850); Nees Ton Esenbeck, "Das System der Pilze" (1816); Bonorden, "Handbuch der Allgemeinen Mykologie" (1851).

VII.

GERMINATION AND GROWTH.

In describing the structure of these organisms in a previous chapter, the modes of germination and growth from the spores have been purposely excluded and reserved for the present. It may be assumed that the reader, having followed us to this point, is prepared for our observations by some knowledge of the chief features of structure in the principal groups, and of the main distinctions in the classification, or at least sufficient to obviate any repetition here. In very many species it is by no means difficult to induce germination of the spores, whilst in others success is by no means certain.

M. de Seynes made the Hymenomycetes an especial object of study, but he can give us no information on the germination and growth of the spore. Hitherto almost nothing is positively known. As to the form of the spore, it is always at first spherical, which it retains for a long time, while attached to the basidia, and in some species, but rarely, this form is final, as in Ag. terreus, &c. The most usual form is either ovoid or regularly elliptic. All the Coprini have the spores oval, ovoid, more or less elongated or attenuated from the hilum, which is more translucent than the rest of the spore. This last form is rather general amongst the Leucospores, in Amanita, Lepiota, &c. At other times the spores are fusiform, with regularly attenuated extremities, as in Ag. ermineus, Fr., or with obtuse extremities, as in Ag. rutilans, Sch. In Hygrophorus they are rather irregular, reniform, or compressed in the centre all round. Hoffmann has given a figure taken from Ag. chlorophanus, and Seynes verified it upon Ag. ceraceus, Sow. (See figures on page 121.)

The exospore is sometimes roughened, with more or less projecting warts, as may be seen in Russula, which much resembles Lactarius in this as in some other particulars. The spores of the Dermini and the Hyporhodii often differ much from the sphærical form. In Ag. pluteus, Fr., and Ag. phaiocephalus, Bull, there is already a commencement of the polygonal form, but the angles are much rounded. It is in Ag. sericeus, Ag. rubellus, &c., that the polygonal form becomes most distinct. In Dermini the angles are more or less pronounced, and become rather acute in Ag. murinus, Sow., and Ag. ramosus, Bull. The passage from one to the other may be seen in the stellate form of the conidia of Nyctalis.

It is almost always the external membrane that is coloured, which is subject to as much variation as the form. The more fine and more delicate shades are of rose, yellow-dun or yellow, violet, ashy-grey, clear fawn colour, yellow-orange, olive-green, brick-red, cinnamon-brown, reddish-brown, up to sepia-black and other combinations. It is only by the microscope and transparency that one can make sure of these tints; upon a sufficient quantity of agglomerated spores the colour may be distinguished by the naked eye. Colour, which has only a slight importance when considered in connection with other organs, acquires much in the spores, as a basis of classification.

With the growth of Agarics from the mycelium, or spawn, we are not deficient in information, but what are the conditions necessary to cause the spores themselves to germinate before our eyes and produce this mycelium is but too obscure. In the cultivated species we proceed on the assumption that the spores have passed a period of probation in the intestines of the horse, and by this process have acquired a germinating power, so that when expelled we have only to collect them, and the excrement in which they are concealed, and we shall secure a crop. As to other species, we know that hitherto all attempts to solve the mystery of germination and cultivation has failed. There are several species which it would be most desirable to cultivate if the conditions could be discovered which are essential to germination. In the same manner the Boleti and Hydnei--in fact, all other hymenomycetal fungi, with the exception of the Tremellini--still require to be interrogated by persevering experiment and close inquiry as to their mode of germination, but more especially as to the essential conditions under which alone a fruitful mycelium is produced.

The germination of the spore has been observed in some of the Tremellini. Tulasne described it in Tremella violacea. These spores are white, unilocular, and filled with a plastic matter of homogeneous appearance. From some portion of their surface an elongated germ filament is produced, into which the contents of the reproductive cell pass until quite exhausted. Other spores, perhaps more abundant, have a very different kind of vegetation. From their convex side, more rarely from the outer edge, these particular spores emit a conical process, generally shorter than themselves, and directed perpendicularly to the axis of their figure. This appendage becomes filled with protoplasm at the expense of the spore, and its free and pointed extremity finally dilated into a sac, at first globose and empty. This afterwards admits into its cavity the plastic matter contained in its support, and, increasing, takes exactly the form of a new spore, without, however, quite equalling in size the primary or mother spore. The spore of the new formation long retains its pedicel, and the mother spore which produced it, but these latter organs are then entirely empty and extremely transparent. Sometimes two secondary spores are thus engendered from the same spore, and their pedicels may be implanted on the same or on different sides, so as to be parallel in the former case, and growing in opposite directions in the latter. The fate of these secondary spores was not determined.

In Dacrymyces deliquescens are found mingled amongst the spores immense numbers of small round or ovoid unilocular bodies, without appendages of any kind, which long puzzled mycologists. Tulasne ascertained that they are derived from the spores of this fungus when they have become free, and rest on the surface of the hymenium. Each of the cells of the spore emits exteriorly one or several of these corpuscles, supported on very short slender pedicels, which remain after the corpuscles are detached from them. This latter circumstance evidences that new corpuscles succeed the firstborn one on each pedicel as long as there remains any plastic matter within the spore. The latter, in fact, in consequence of this labour of production, becomes gradually emptied, and yet preserves the generative pedicels of the corpuscles, even when it no longer contains any solid or coloured matter. These pedicels are not all in the same plane, as may be ascertained by turning the spore on its longitudinal axis; but it often seems to be so when they are looked at in profile, on account of the very slight distance which then separates them one from another. It will also be remarked that they are in this case often implanted all on the same side of the reproductive body, and most often on its convex side. Their fecundity is exhausted with the plastic contents of the spore. The corpuscles, when placed in the most favourable conditions, have never given the least sign of vegetation; they have also remained for a long time in water without experiencing any appreciable alteration.

All the individuals of Dacrymyces deliquescens do not produce these corpuscles in the same abundance; those which bear the most are recognizable by the pale tint of the reproductive dust with which they are covered; in others, where this dust preserves its golden appearance, only a few corpuscles are found. The spores which produce corpuscles do not appear at all apt to germinate. On the other hand, multitudes of spores will germinate which had not produced any corpuscles. Tulasne remarks on this, that these observations would authorize us to think that all spores, though perfectly identical to our eyes, have not, without distinction, the same fate, nor doubtless the same nature; and, in the second place, that these two kinds of bodies, if they are not always isolated, yet are most frequently met with on distinct individuals. This author claims for the corpuscles in question that they are spermatia, and thinks that their origin is only so far unusual in that they proceed from veritable spores.

The whole of the Gasteromycetes have as yet to be challenged as to the mode and conditions of germination and development. It is probable that these will not materially differ from those which prevail in Hymenomycetes.

The germination in Æcidium has been followed out by Tulasne, either by placing the pseudospores in a drop of water, or confining them in a moist atmosphere, or by placing the leaves on which the Æcidium flourishes upon water. The pseudospores plunged in water germinated more readily than the others. If the conditions were favourable, germination would take place in a few hours. Æcidium Ranunculacearum, D. C., on leaves of figwort, gives rarely more than one germinating filament, which soon attains three times the length of the diameter of the pseudospore. This filament generally remains simple, sometimes torulose, and distorted in a long spire. Sometimes it has been seen divided into two branches, nearly equal to each other. The spore in germinating empties itself of its plastic contents, contracts, and diminishes in size. The pseudospores of Æcidium crassum, P., emit three long filaments, which describe spirals, imitating the twistings of the stem of a bean or bindweed. In Æcidium Violæ, Schum, one filament is produced, which frequently rolls up its anterior extremity into a spire, but more often this same extremity rises in a large ovoid, irregular vesicle, which continues the axis of the filament, or makes with it a more or less decided angle. In whatever manner placed, this vesicle attracts to it all the orange protoplasm, and hardly does this become settled and complete before the vesicle becomes the starting point of a new development, for it begins to produce at its apex a filament, more slender than the previous one, stiff, and unbranched.

According to M. Tulasne, the germination of the pseudospores of Æcidium Euphorbiæ on Euphorbia sylvatica differ in some respects from the preceding. When dropped upon water these spores very soon emit a short tube, which ordinarily curves in an arch or circle, almost from its origin, attaining a length of from three to six times the diameter of the spore; then this tube gives rise to four spicules, each of which produces a small obovate or reniform sporule; the generation of these sporules absorbs all the plastic matter contained in the germ-tube, which permits of the observation that it was divided into four cells corresponding with the number of spicules. These sporules germinate very rapidly from an indefinite point of their surface, emitting a filiform process, which is flexuous and very delicate, not extending more in length than three times that of the long axis of the sporule, often less, reproducing at its summit a new sporule, differing in form and size from that which preceded it. This sporule of the second formation becomes at its apex a vital centre, and sprouts one or more linear buds, of which the elongation is occasionally interrupted by the formation of vesicular swellings. As Tulasne observes, the pseudospores of the Æcidium and the greater number of Uredines are easily wetted with water before arriving at maturity; but when they are ripe, on the contrary, they appear to be clothed with a greasy matter which protects them from the liquid, forcing them almost all to rest on the surface.

The pseudospores of Roestelia are produced in strings or chaplets, as in Æcidium, with this difference, that instead of being contiguous they are separated by narrow isthmuses. The ripe pseudospores are enveloped in a thick tegument, of a dark brown colour. They germinate readily on water, producing a filament fifteen times as long as the diameter of the spore. This filament is sometimes rolled or curved. Towards its extremity it exhibits protuberances which resemble the rudiments of ramuli, or they terminate in a vesicle which gives rise to a slender filament. The tegument of these pseudospores, above all in those which have germinated, and have consequently become more transparent, it is easy to see has many pores, or round ostioles.

In Peridermium the pseudospores, when dropped upon water, germinate at any point of their surface. Sometimes two unequal filaments issue from the same spore. After forty-eight hours of vegetation in the air, the greater part had already emitted a multitude of thick little branches, themselves either simple or branched, giving to the filaments a peculiar aspect. Tulasne did not on any occasion observe the formation of secondary spores.

In the Uredines proper the germination seems to be somewhat similar, or at least not offering sufficient differences to warrant special reference in Uredo, Trichobasis, Lecythea, &c. In Coleosporium there are two kinds of spores, one kind consisting of pulverulent single cells, and the other of elongated septate cells, which break up into obovate joints. Soon after the maturity of the pulverulent spores, each begins to emit a long tube, which is habitually simple, and produces at its summit a reproductive cellule, or reniform sporule. The orange protoplasm passes along the colourless tubes to the terminal sporule at the end of its vegetation. The two forms of spores in this genus are constantly found on the same leaf, and in the same pulvinule, but generally the pulverulent spores abound at the commencement of the summer. The reniform sporules begin to germinate in a great number as soon as they are free; some few extend a filament which remains simple and uniform, but more commonly it forms at its extremity a second sporule. If this does not become isolated, to play an independent life, the filament is continued, and new vesicles are repeated many times.

In Melampsora the summer spores are of the Lecythea type, and were included in that genus till their relation with Melampsora was clearly made out. The winter spores are in solid pulvinules, and their fructification takes place towards the end of winter or in the spring. This phenomenon consists in the production of cylindrical tubes, which start from the upper extremity of the wedge-shaped spores, or more rarely from the base. These tubes are straight or twisted, simple or bifurcated, and each of them very soon emits four monosporous spicules, at the same time that they become septate. The sporules are in this instance globose.

In Uromyces germination follows precisely the same type as that of the upper cell of Puccinia; in fact, Tulasne states that it is very difficult to say in what they differ from the Pucciniæ which are accidentally unilocular.

In Cystopus a more complex method prevails, which will be examined more closely hereafter.

In Puccinia, as already observed when describing their structure, the pseudospores are two-celled. From the pores of each cell, which are near the central septum, springs a clavate tube, which attains two or three times the total length of the fruit, and of which the very obtuse extremity curves more or less in the manner of a crozier. This tube, making a perfectly uncoloured transparent membrane, is filled with a granular and very pale plastic matter at the expense of the generative cell, which is soon rendered vacant; then it gives rise to four spicules, usually on the same side, and at the summit of these produces a reniform cellule. The four sporules so engendered exhaust all the protoplasm at first contained in the generative cell, so that their united capacity proves to be evidently much insufficient to contain it, the more so as it leads to the belief that this matter undergoes as it condenses an elaboration which diminishes its size. In all cases the spicule originates before the sporule which it carries, and also attains its full length when the sporule appears. The form of the latter is at first globular, then ellipsoid, and more or less curved. All these phases of vegetation are accomplished in less than twelve hours, and if the spore is mature and ready for germination, it is sufficient to provoke it by keeping the pseudospores in a humid atmosphere. During this process the two cells do not separate, nor does one commence germination before the other, but both simultaneously. When the sporules are produced, the protospore, somewhat analogous to a prothallus, has performed its functions and decays. Towards the time of the falling of the sporules they are nearly all divided into four unequal cells by transverse and parallel septa. These sporules in time produce, from any point on their surface, a filament, which reproduces a new sporule, resembling the first, but generally smaller. This sporule of the second generation ordinarily detaches itself from its support before germinating.

The pseudospores of Triphragmium ulmariæ have been seen in April germinating on old leaves of the meadowsweet which survived the winter, whilst at the same time new tufts of the spores were being developed on the leaves of the year. These fruits of the spring vegetation would not germinate the same year. Each cell in germination emits a long cylindrical filament, containing a brownish protoplasm, on which four spicules, bearing as many sporules, are generated.

The germination of the black fruits of Phragmidium only appears to take place in the spring. It greatly resembles that in Puccinia, except that the filament is shorter, and the sporules are spherical and orange-coloured, instead of being kidney-shaped and pale. In the species found on the leaves of the common bramble, the filament emitted by each cell attains three or four times the length of the fruit. The granular orange protoplasm which fills it passes ere long into the sporules, which are engendered at the extremity of pointed spicules. After the long warty fruits are emptied of their contents they still seem as dark as before, but the pores which are pierced in the sides, through which the germinating filaments have proceeded, are more distinctly visible.

It will be observed that throughout all these allied genera of Uromyces, Puccinia, Triphragmium, and Phragmidium the same type of germination prevails, which confirms the accuracy of their classification together, and renders still less probable the supposed affinity of Phragmidium with Sporidesmium, which was at one time held by very astute mycologists, but which is now abandoned. This study of germination leads also to a very definite conclusion with regard to the genus Uromyces--that it is much more closely related to Puccinia and its immediate allies than to other unicellular Uredines.