of Lichens.

BY REV. W. JOHNSON.

(Concluded from page 183.) Having, though but in a very limited way, touched upon the chief features of the Lichen-thallus, we must now endeavor to convey an idea of its reproductive system. Lichens are said to have many modes of reproduction. Körber enumerates six. Two by spores and four by gonidia. But without accepting that statement, the

FIG. 46.

Lichen undoubtedly has a secondary, or indirect method, of reproducing itself, by its green cells or gonidia. Still, whether the gonidial cell alone can produce a perfect plant, that is, a plant which will bear fruit and develop spores, we have not yet seen authenticated. The proper and normal way of fructification in the Lichen, is by sporidia. These are developed in a special organ adapted for their formation, protection, maturity and

denominated the apothecium. (Gr. apotheke, a storehouse or repository.) It is always found upon the surface, or attached to the margin of the thallus. It may be sessile resting upon the surface; innate sunk in the thallus; stipitate on little stalks, or surmounting the top of podetia. These latter are cylindrical and vertical prolongations of the thallus, crowned with a cuplike cavity, on the toothed margins of which grow the apothecia, as in Cladonia. In some cases the cup is substituted by globose fruit, singly or conglomerate. The apothecium assumes many different shapes on different plants. It is typically round and flat, or slighly concave when it is termed scutellate. Sometimes it rises up from the margin of the thallus like a target, as in Peltigera; then it is peltate. At other times, it is oblong and furrowed; when it is called lirellate. It also appears like a little wart upon the thallus, then it is verrucose. Besides these, there are other forms. The structure of the apothecium is the most complex part of the plant; and it is beautiful in its arrangement, as well as efficiently adapted for its purpose of maturing and protecting the spores. The apothecium consists of two parts an excipulum and a nucleus, called the hymenium. The excipulum is the outer covering, or envelope of the apothecium. It is seen encircling, or more or less enclosing the fruit. When it is of the same texture and color as the thallus it is termed a thalline excipulum. But when

it differs from the thallus, and partakes more of the color of the nucleus, it is a proper excipulum. The hymenium, or thalamium, is the centre of the fruit organ, and is easily recognized by its color and gelatinous appearance. It embraces the paraphyses, asci and spores. The paraphyses (6 Fig. 46) are long, slender, cylindrical, hyaline, cells, or filaments; swollen at the apices into the shape of a club, where they are also frequently of a dark or pale color. They grow upright or vertical from a bed of cells, known as the hypothecium, (4 Fig. 46), and stand like corn in a field, only closer together. Their apices are glued into a solid mass, and form what is called the epithecium, or disc of the fruit. The direct function of the paraphyses is not clearly understood; but it is, without doubt, to subserve the spores. By their agglomeration, they retain around the asci, if they do not secrete it, a large quantity of lichenine, which helps the nourishment of the young sporidia. They also hold up the asci in a vertical position, when being full of spores, they would otherwise fall down upon the hypothecium; and when the asci and spores are ripe they act as a sort of spring upon them, caused by the expansion and contraction of damp and dry weather. The spores are thus, by pressure, expelled into the air through the disc or epithecium; when the wind wafts them on, to grow in new spheres. The asci or thecæ (5 Fig. 46), are large vesicles or sacs, growing upright among the paraphyses from the hypothecium. They are in shape oblong, pyriform, linear or clavate; but always tapering off at the base. They are closely pressed by the paraphyses, from which they differ by being broader and inferior in length. The spores are formed and matured in these sacs; and when ripe, by the lateral pressure of the paraphyses, or the internal pressure of the spores, or from both, the ascus ruptures at the apex, and the spores, are liberated. The spores (Gr. spora,

a seed), Fig. 46, is the reproductive germ. It is formed in the ascus from protoplasmic-lichenine

a

matter.

When mature, it consists of a cell having an inner and outer wall, termed respectively, the endosporium and episporium. It is frequently divided by septa into two or more cells. The spores are generally eight in number, in each ascus ; but some of the larger spored forms, as Pertusaria, produce in the spore-sac four, two, and sometimes only one spore, while on the other hand, in minute spored species, they are innumerable. The form and color of the spores are very much disversified. They range from globose to fusiform and acicular. That is, from round to spindle and needleshape. Their color is from a pale greenish or yellowish tinge, to a dark olive or deep brown.

Composed of these several parts, the apothecium constitutes the female organ of the fructification, the spores of which are fecundated by the minute bodies next to be described; but how, or in what way, this fecundation is affected, has not yet been discovered. The fecundating bodies are termed spermatia. They are very minute rod-like, or oval organs, varying in length and breadth; and are sometimes bent or curved; they are uncolored and transparent. These organs are produced in small cavities, sunk or immersed in the Lichen-thallus; and opening on its surface by a small pore. These cavities or cysts are called spermogones. (Fig. 47).

They sometimes require a lens to discover them; but, on some thalloidal forms they are plain and prominent. As, for instance, the laciniæ, of certain Ramalinas, and the fronds of Ricasolia amplissima. The interior of the spermogonic cell is composed of a number of delicate, elongated filaments, all growing from the walls of the vesicle, and at once projecting and converging into the centre of it. These filaments are denominated sterigmata (Gr. sterigma, a prop or support) from the fact that they bear the spermatia. The sterigmata are sometimes simple or articulate and branched, and they bear the spermatia on their sides or apices. The contents of the spermogones, like those of the apothecia, are truly lichenose, being filled and bathed with lichenine. Perhaps, we should mention another minute organ found upon the Lichen, and named pycnides. These externally resemble spermogones, and only a microscopical examination can distinguish them. They differ, however, in their internal growth. Instead of sterigmatic filaments, they contain simple, short, thickish stalks, or stoutish cells, called basidia, which generate and bear on their apices stylospores. These are pyriform or oval bodies, something like ordinary spores. The function

of pycnides, like that of spermogones, is still very much shrouded in mystery, and until this is understood, we cannot truly know the real difference between them. They are illustrated by Fig. 48.

FIG. 48.

We have already hinted that the Lichen has no axis and no root. Therefore it does not nourish itself from the soil, or place of growth. It is an aerial plant, and what the water with its solutions is to the Alga, the damp atmosphere is to the Lichen. The whole plant imbibes nourishment alike, and its growth is, therefore, much affected by the purity, dryness, or humidity of the air. A polluted atmosphere is destructive to Lichen growth, while a flourishing condition of these plants, is a sure indication of the purity of the surrounding aerial medium. On account of their spongy, cellular nature, Lichens are strongly hygrometric. After being in the herbarium for years, on the application of moisture which they greedily absorb, they will freshen up and appear almost as bright and green as when first gathered. While humidity promotes their growth yet they are capable of enduring great drought. The crustaceous Lichens are of very slow, and frequently very long, growth. Some are said to grow for hundreds of years. They cover, and emboss in grey and gold, the rocks on our highest mountains; to which they cling so closely, that no storm affects them. The foliaceous plants, contrary to the crustforms, attain their highest development at low altitudes, and in shaded places. Some of the softer and less thalline plants grow to maturity in a short space of time. I gathered myself, Odontotrema longius (Nyl.), in considerable quantity on an old rail, near Asby, Cumberland, in the autumn of 1879. In the same month of last year (1880), I visited the same spot, and upon the old cuttings of the previous year, upon the very knife marks, I found the same plants regrown. No thallus was visible, but some of the apothecia, when examined under the microscope, were fully developed. This growth of the Lichen had been made in one year.

The habitats of Lichens are almost all objects on the surface of the earth.

They grow abundantly on rocks, old stumps, exposed tree roots, the withered fronds of ferns, on mosses, sheep's dung, mortar, and some have been found on glass. They are natives of the whole country side.

"With such a liberal hand has Nature flung Their seeds abroad, blown them about in winds." Although our remarks partake more of the character of hints than full statements, yet, on account of their length already, we must at present omit noticing the uses and applications of Lichens, with their classification and geographical distribution ; and we must proceed to give a few suggestions on the method of studying this group of plants. Now, the thing of primary importance in the study of any subject, is a definite object. To fritter away our time over a score of different things, answers no purpose beyond a momentary gratification in our own mind. It leaves no permanent results, nor deep sense of satisfaction. We must select where the subjects before us are so many. Our selection should be made with due regard to the tastes and idiosyncrasies of our own minds, and the favorableness of our circumstances for the pursuit. With definite aim and concentration of powers, we are sure to work to some good end. Further, it is not desired that any student of Nature should content himself with being merely a collector, classifier, or herbarium-maker; but that he should seek a more intimate acquaintance with things. Knowledge is only sound and good in proportion as it is profound; for it is only when we know the nature of things, that we can assign them their proper place in systems, or increase their useful application in daily life. In the study of Lichens, the first thing needed is a text book, or some source where we can obtain a sufficient knowledge of the plants, as to become a starting point for our own observations. The meagre notice taken of Lichens in most Manuals of Botany, is of little or

no use. Hitherto, it has hardly seemed to come within the aim of books of that class, to acquaint any one with our Cryptogamia; and Lichens, more then any other group of plants, have been ignored or neglected by them. The best book, and the only suitable one we have at present for a beginner in Lichenology, is "A Popular History of British Lichens," by Dr. W. L. Lindsay. This book is simply and well written, also beautifully illustrated. It costs about seven shillings. After that, "A Manual of British Lichens," by W. Mudd, is a good work, but it is scarce. The chief book on the subject is "The LichenFlora of Great Britain, &c.," by Rev. W. A. Leighton, 3d Ed., 1879. Price This last work can only be used after some acquaintance with the subject. In addition to the literature mentioned, the student will find great help from the possession or access to a series of dried specimens.

2IS.

After the reading and study of the text book, plants may be gathered. For this purpose you may have to go a considerable distance from home; but begin collecting nearest home first. As you acquaint yourself with the plants nearest your own immediate neighborhood, then widen your area of search. Select a fine day for collecting. A little damp in the air will be an advantage; because some gelatinous and foliaceous Lichens growing on stones, if very dry, are apt to break and crumble in gathering. When in that condition, we have sometimes sprinkled them with water from an adjoining stream; and in a minute or two, they have yielded beautifully to the broadish point of the knife beneath them. Specimens should always be gathered, if possible, in fruit; and as near complete as can be. Preparations should be made for this out-door work. Put on clothes which will neither trouble nor deter you from thrusting yourself into any corner. Let your boots be such as will cross swampy ground, or dip into a stream without discomfort. You will

also require a pocket lens; a hammer, and two or three mason's chisels. If you carry only one chisel, and have to face hard rocks, during the first fifteen minutes you may find yourself half helpless for the rest of the day, by the turning or breaking of your chisel point. Crustaceous Lichens are gathered by cutting away a piece of the stone on which they grow, and the other forms accordingly. You will further need a botanical box, or small basket, and many of the specimens will require wrapping in paper, to prevent rubbing, in carrying them home. Take particular note where the plants are gathered, so that the locality in a word or two can be written upon the sheets when they are mounted.

On reaching home with your gatherings, the first thing to be done is to press and dry the foliaceous and fruticulose forms. Then mount the whole on slips of paper, with gum or glue. We find nothing to answer this purpose better than a thick solution of gum Arabic, with a few drops of glycerin in it, to modify its brittleness. On each slip of paper record the place where gathered, with date, and collector's name. The plants may now be placed together on one side without danger of confusion, and be brought out one by one for determination or study as you may have leisure and opportunity. In the investigation of Lichen tissues and sporidia, and the determination of species, there will be required a compound microscope, with a magnifying power of from 60 to 400 linear measurement (one-inch and quarter-inch objectives with A and C eye-pieces); also, a double lens for the eye. Some use an ordinary watchmaker's eyeglass. One of these glasses mounted in a pair of spectacle frames, would be very useful for the lichenologist. A small thin dissecting knife, and solutions of iodine, hydrate of potash, and hypochlorite of lime. The making up, with the application of these reagents, are fully described in

Leighton's Lichen-Flora. The iodine acts more or less upon the gelatinahymenea of the paraphyses and asci, turning them blue, yellow, or vinousred. The hydrate of potash dissolves the gelatina-hymenea, and shows the hymenium more clearly under the microscope, beside swelling the spores and paraphyses up to their full size. The hydrate of potash and hypochlorite of lime are also used on the Lichen-thallus as tests; and, as such, are of considerable value and importance. On account of the chemical elements in the thallus, it reacts in certain colors, or not, on the application of these reagents. This reaction, or non-reaction, is a great help in the determination of species. The method of examining the apothecium or other organ of the Lichen, is to place the plant on the table, then, with the lens to the eye, place the knife on the top of the organ about midway, and cut it straight down. Cut down a second time close to the first, and thus get out a section as thin as you possibly can; place it in the compressor, or upon the glass stage of the microscope, moisten it with clear water, and put on a thin glass cover. Now you may examine the section, and if you have a good cut, you will have all the parts of the apothecium before you. You must now observe the color and form of the hypothecium, the character of the paraphyses, with the color of their apices; also, the shape of the asci, and the number, color, form and septa of the spores. You may now run in a drop of iodine, watch and carefully note the results. After this, run in a drop of the hydrate solution, which will annul the action of the iodine-consequently it must always be used after it, where both are required. This does not generally destroy any natural color, but it will show you, if you have obtained a correct idea of the several points just named above. When you have thus examined the apothecium, and the spermogones if you can find any; and