OF THE ANNULUS, THE VELUM, AND THE VOLVA.
Of these involucra the first two are partial, the other universal. The Volva is a thick membranaceous covering, originating at the base of the fungus, which it thus connects with the earth, and furnishes, during its fœtal life, with the means of support and nourishment. When this has ceased, and the plant has quitted its wrapper, if this still adhere to the base of the stalk, it is styled manifest (manifesta), but if there be no traces of it left, obliterated (obliterata). It is free when it can be easily detached, and congenital when it cannot without laceration. In funguses with bulbous roots it is congenital, in those without bulbs it is free. All funguses that have a volva are of course volvati, but as this organ exists in many only so long as they are underground, mycologists are agreed to restrict the term to such alone as retain it afterwards.
The Ring.—This, which differs considerably in form, substance, and in its attachments, is composed either of a continuous sheet of membrane or else of a number of delicately-spun threads, resembling a spider’s web,[113] which in either case passing from the margin of the pileus to the corresponding upper portion of the stem, give way as the plant expands, and either festoon for a season the margin of the cap, or encircle the stalk with a ring. The marginal remains of the Annulus are extremely fugacious, but the ring round the stalk, though generally transitory, is sometimes persistent; it is superior or descending when originating from the summit of the stem, it descends outwards and downwards to form connections with the rim of the pileus; inferior or ascending when, coming off from that portion of the stalk which is below the pileus, it ascends to attach itself to this. In a few cases the ring is partly membranaceous and partly composed of radiating arachnoid threads.
The Veil.—Some funguses not only present the ring just mentioned, their hymenium or seed membrane being further protected from harm by a second investment, the veil, Velum, the stalk origin of which, when existing in conjunction with an annulus, is below it, but when the fungus is not annulate, the velum rises higher up on the stalk, stretches across to meet and is afterwards reflected over the whole surface of the pileus; on the expansion of the Agaric this investment is entirely broken up, and exhibits those well-known flocks, which have been called by the learned verrucæ, but which, as they are generally of a dirty leprous hue, and affect more or less of a circular arrangement, have procured for this whole tribe of Amanites in Italy the uncomely epithet of tignosi, or scald-heads. Where there has been both a volva and a velum, as sometimes happens in the same fungus, these verrucæ are of different colours according as they are remnants of the first merely, or of both together.[114] The velum in the subgenus Limacium is a slimy coating adhering to the head of the fungus, which then looks as if it had been dipped in gum mucilage; this generally disappears after a time, leaving the epidermis dry, though sometimes, like the solid membranaceous veil, it is more or less persistent. The waxy covering on the pileus of the Ag. virescens, which after a time cracks and tessellates its surface, is only an exudation limited to the upper portion of the cap, and not a veil.
The Stalk.—This, which is absent in many parasitical funguses of the Order Pileati, when present, either effuses itself uninterruptedly into the substance of the pileus, which it then, in fact, forms, or else supports merely as on a pillar, a distinct line of demarcation showing where the fibres terminate. It assumes a great variety of forms, which serve in many instances to characterize species; besides which peculiarities there are others to be noted, as the mode of its insertion into the pileus, its having or not having a ring, the circumstance of its being scabrous, glossy, or tomentose, reticulated, spotted, or striped, of one colour above and another below, or of its changing colour when bruised, any of which may sometimes assist our diagnosis.
The Pileus.—By far the larger number of funguses mentioned in this work have a pileus, or cap; all such belong to the first great tribe Pileati; they include the genera Agaricus, Boletus, Cantharellus, Morchella, Hydnum, Fistulina, and Polyporus, each of which furnishes its quota of alimentary species, together with many others not esculent. The form of the pileus, like that of the stalk, is various in these different genera, besides being variable in the different species of the same genus; generally it assumes an orbicular or umbrella shape, especially in such funguses as grow solitary on the ground, whilst in others, parasitical on trees, (particularly when they have no stalk,) it is more or less of a half-hemisphere.
The Gills.—Those vertical plates on the under surface of the mushroom, which radiate from the centre to the circumference, like the spokes of a wheel, are called Gills (lamellæ); they are not formed, as some have supposed, of layers of the reduplicated seed-membrane alone, but by a prolongation of the fibres of the pileus, which these merely invest. The fibrous structure is most apparent in Agarics with thick gills; in those where the flesh changes colour when bruised; or where, the interposed flesh remaining white, the hymenium is tinged with the colour of the ripening spores. In those funguses which have little flesh the upper surface of the pileus, especially towards the circumference, is frequently furrowed with transverse sulci; these are occasioned by the sinking in of the epidermis along with the fibres of the flesh between the layers of the hymenium, and consequently their position always corresponds precisely to that occupied by the backs of the gills. The end nearest the stalk is termed posterior (postica), the opposite extremity anterior (antica); the terminations of the lesser gills take place at various distances short of the stalk, which the perfect gills reach, and down which they sometimes course or are decurrent (decurrentes); they are said to be adnate (adnatæ) when connected at their posterior end; free (liberæ) when they do not adhere; remote (remotæ) when they terminate at a certain distance from the stem; emarginate (emarginatæ) when they are obtusely notched or hollowed out posteriorly; denticulate (denticulatæ) when connected by means of a tooth; equal (æquales) when all of the same length; forked (furcatæ) and branched (ramosæ) when they divide in their course, once, or more frequently, or are connected at the sides with the imperfect gills; dedalean (dædaleæ) when they anastomose irregularly together; simple (simplices) when they are free from all connections; distant (distantes) when they are few and wide apart; close (confertæ) when they are very numerous and touch each other; serrated (serratæ) when notched like a saw; waved (undulatæ) when the margin is undulating; and imbricating (imbricatæ) when they lie one over another, like tiles.
The Tubes.—Funguses of the genus Boletus, etc., present on their under surface, in place of gills, series of small hollow cylinders or tubes; which are for the most part soldered side to side like the cells of a honeycomb, but in the Fistulina are unconnected. Like the gills, they are prolongations of the fibres of the pileus, but lined, instead of coated, by the hymenium; their free extremities are the pores, which at first are closed, but afterwards open to let the seed escape: they are generally of equal length and simple, but sometimes in the interior of a large one smaller tubes may be discerned, in which case the first is termed compound. With reference to the stalk, they are either adnate or decurrent, they first appear as a network formed by slight prominences of the fibres of the pileus; if at this early period a portion be removed together with a piece of the flesh, it is reproduced in a few days and the tubes developed as usual. The beautiful reticulations observed on the stalk of some Boletuses are produced by abortive tubes decurrent along their surface.
The Plaits: Venæ, Plicæ.—The plaits of the Chanterelle are formed like the gills and tubes of the mushroom and Boletus, i. e. by the fibres of the flesh running down from the pileus, and invested in a reduplication of the hymenium; with this difference, however, that while in the two latter the seed membrane is divided into as many portions as there are gills or tubes, in the former the continuity of its surface is perfectly unbroken. These plaits (plicæ) are always late in appearing, and sometimes are only developed when the fungus is about to cast its seed.
The Spines: Aculei, etc.—The under surface of the pileus in the genus Hydnum is shagged with vegetable spines or teeth (dentes, aculei) of unequal lengths, generally isolated, but sometimes connected at the base, and formed originally out of a congeries of minute papillæ invested by the hymenium, which gradually elongate their fibres and assume this form. Light seems essential to their production, for if a Hydnum grow in the dark, the teeth shrink up into long threads and are sterile.