LESSONS IN BOTANY. 



33 



LESSONS IN BOTANY. XLH. 



SECTION CXXII. LICHENS. 



I UK structure of Lichens ia Tory dimple, and they ooonpy nearly 

 the lowest station in the scale of vegetation, tint Fungi alone 

 ranking below them. Their origin in some situations is bun<-<l 

 in mystery ; somo have even supposed that certain kinds are of 

 m. t.-..n< (in.'luction, a theory supposed to be supported by the 

 facts (as stated by Fries) that the leaves of some pines near 

 iden were suddenly covered, on the side next the wind, with 

 A species of lichen ; and also that on a hot summer's day the 

 Huilrt and masts of a ship at Stockholm were instantaneously 

 covered with a coating of a similar character. 



Lichens .iro the first examples of vegetation found on many 

 bare rooks in newly-formed islands. How their spores can have 

 been convoyed to euoh now and remote positions it is impossible 

 to say; but truly "there are more things in heaven and earth 

 than are dreamt of in onr philosophy ! " Even in the present 

 day, when painful and diligent research has thrown light on so 

 many subjects which were formerly wrapped in apparently im- 

 penetrable darkness, how much of interest yet remains to be 

 lii.-i.!.ii..il ; how many discoveries are doubtless yet in store to 

 reward the earnest and sedulous student of Nature ! Yet, 

 search as wo will, depths will still remain unfathomed, for " who 

 can search out the Almighty unto perfection ?" 



I-ii'ln'iis exist exclusively on atmospheric supplies, requiring 

 only air, sunlight, and some degree of moisture 

 for their support. The simplicity of their struc- 

 ture enables them to exist at altitudes where the 

 air is too thin for the support of plants of the 

 higher orders of vegetation, so that theyare fonnd 

 in abundance even at the very verge of the limits 

 of perpetual snow. Lichens, with mosses, serve 

 as pioneers of vegetation, having the power of 

 acting on the stones and rocks below them, so 

 as to produce small hollows in which moisture 

 collects ; then comes the frost, that seizes on 

 the moisture which has forced its way into the 

 little crevices already formed, and splits the 

 rock, so as to cause it to moulder away ; and 

 this process, which is continually going forward, 

 by degrees prepares a soil fit for the nourish- 

 ment of larger plants. 



A lichen has neither root, stem, nor branches ; 

 it consists of a dry, scaly crust, which some- 

 times appears almost like a mere powder, but in others extends 

 itself into broad curled surfaces called thalli, which have some- 

 what the appearance and perform the functions of stems and 

 leaves. It bears no flower, but produces abundance of fruit ; 

 this consists of a multitude of spores, which are enclosed in 

 cases differently disposed on the margin of the thallus, or else 

 growing from or embedded in its surface. These are immersed 

 in shields, or cup-like receptacles, which are called apothecia, 

 from the Greek airoOriKi) (ap-o-the'-kc), which means a repository, 

 *nd arc frequently raised on a sort of foot-stalk termed apodetia. 



Lichens have been classed under five tribes : 1st, the Idio- 

 ihalami, consisting of those whose apothecia or receptacles 

 differ in colour from the rest of the plant, and are formed of a 

 different substance ; 2nd, the Ccenothalami, which are those 

 where the apothecia are partly formed from the substance of 

 *he thallus ; 3rd, the Homothalami, where the apothecia are 

 entirely formed of and of the same colour as the frond or 

 thallus ; 4th, the Athalami, whose fructification is unknown, 

 they being wholly destitute of apothecia ; and the 5th and last 

 tribe, which are called Pseudo-Lichenes, are those in which the 

 apothecia are black and horny, and embedded in a receptacle, 

 their spores contained in slender tubular cells lying in a pulp, 

 and not spontaneously emitted ; these have usually been classed 

 as fungi, and are in many respects like them. There are 

 numerous sub-divisions of these tribes, which we must not 

 attempt to describe, as it would lead us far beyond the limits 

 of our space ; neither would it avail us to attempt to follow the 

 learned investigations which have of late been entered into 

 concerning the formation and arrangement of the spores in the 

 different genera, as detailed in a work written by the Rev. W. A. 

 Leighton, and published under the auspices of the Ray Society. 

 Our endeavour must rather be to open the eyes of our readers 

 to the outward beauties of this minute tribe of plants ; and to 



107-N.E. 



294. SHIELDED LICHEN (PEL- 

 TIDE A SCUTATA). 



effect this purpose, we must aim at drawing their attention 

 to the appearance and habits of a few of the most common 

 and readily distinguished of the species. Let us, then, take a 

 ramble together through the woods, and over the hill, down 

 to the sea-shore, and we will describe to the reader the objects 

 which we see. 



Observe, as we pass that stone wall, how very richly it v 

 decked with colours ; look at the dark olive and white granu 

 lated substances which in places coat its surface, and the broad 

 patches of orange which vary its tinting, and are themselves so 

 beautifully set off by the soft green of the tufted mosses, now 

 all bristling with capsules ; these are all lichens, and most of 

 them to be classed under onr first bead, as Idiothalami, being 

 formed of a scaly crust, with little receptacles growing out of 

 it ; among these are the Lecideas, Gyrophoras, Endocarpons, 

 and some others ; but although their colouring is vivid and 

 varied, this tribe is so minute that, without a powerful magni- 

 fier, the parts of fructification can scarcely be discerned. But 

 this is not the case with those broad-spreading thalli which lie 

 on the mossy bank at the root of that old oak, weaving them- 

 selves into a mass with the dead leaves which have fallen from 

 its branches. These belong to the genus Peltidea, and form 

 a part of the second and largest tribe of the lichen family, the 

 Ccenothalami, under whose banner are included the greatest 

 number of the most beautiful and conspicuous species of this 

 extended family. These leaves or fronds or, as they are tech- 

 nically termed, thalli belong to the species 

 Peltidea aphthosa, so named from its having 

 been considered by the doctors of ancient days 

 a specific for the complaint called the " thrush," 

 a disease which frequently attacks infants and 

 sometimes adults who have been reduced by fever 

 to a state of great weakness, and which is dis- 

 tinguished by the aphtha or vesicles that form 

 on the lips and in the month, and pass down- 

 wards throughout the alimentary canal. This 

 lichen is of a palo olive green, sprinkled over with 

 brown warts, and underneath whitish, with brown 

 branching veins ; the edge of the thallus being 

 fringed with white cilia; or threads, with which 

 it lays hold of the leaves and mosses below it, 

 and which also probably serve it for the absorp- 

 tion of moisture. If we can find it in fruit, we 

 shall see that some of the lobes of the thallus are 

 drawn up into a sort of foot-stalk, bearing at the 

 point a largo red-brown receptacle. The Peltideas (Fig. 294) are 

 all much of the same character, broadly lobed and fringed, and 

 bearing their fruit in the same manner on the summits of the 

 lobes. Now let us hasten on to the wood. We told you that 

 the trees even in winter were clothed with the most delicate and 

 lovely foliage ; look, then, at that clustering bunch of grey 

 filaments which grows on the branch above you, and observe the 

 broader strap-like kinds some sulphur-coloured, others grey, 

 blackish, or pale green. These are all Lichens, Ramalinas, 

 Usneas, Alectorias, Cornicularias, or others, and all classed 

 under the third head the Homothalami. A little beyond we 

 see the Usnea barbata floating upon the air like an old man's 

 grey beard, and others of the same genus ; and these are again 

 met by other species, so closely clustering that from a little 

 distance the whole tree appears as if covered by a glaucous 

 coating of lichen. There is a very curious species which grows 

 in other lands, the Usnea florida, or flowering lichen. If you 

 gather a piece of it, you will see that it is composed of long 

 branches fringed with fibres of a sort of sea-green, from which 

 proceed at intervals large apothecia, nearly oval in shape and 

 almost as large as a sixpence, flat and edged round with fine 

 ciliro or threads an inch long. Gerard calls this "flouring 

 branched moss," and says, " There is oftentimes found upon old 

 okes, beeches, and such like overgrown trees, a kinde of mosse 

 having many slender branches, which divide themselves into 

 other lesser branches, whereon are placed confusedly very man> 

 small threads, like haires, of a greenish ash-colour. Upon the 

 ends of the tender branches sometimes there cometh forth a 

 floure, in shape like unto a little buckle or hollow mushroom, of a 

 whitish colour tending to yellowness, and garnished with the like 

 leaves of those upon the lower branches." Now examine that 

 beautiful branching liver-wort (Sticta pulmonacea) which runs 

 up the fine dark trunk of that lofty elm. It exhibits a broad 



