LICHEN. 



731 



Conjjli. 



u...... . 



Ueben. neither flowers nor fruit, and the stalks upon which these 

 ""~'"^~ apothecia are elevated arise from a common receptacle. 

 (IKIUDIS of In order distinctly to see the structure of an apothe- 

 iht Apoche- cium, and the parts of which it is composed, it is neces- 

 sary to make a perpendicular section ; and, for this pur- 

 pose, it is right to prepare the specimen by moistening it 

 gradually for some hours. The employment of a pocket 

 lens, or small microscope, is likewise indispensable. 



The apothecia of some lichens are observed at first 

 to be covered with an extremely fine membrane, some- 

 what analogous, it has been thought, to the involucrum 

 or volva of the agarici. But this membrane is not very 

 generally found ; and Acharius considers it as not 

 otherwise useful than in protecting the apothecium 

 when tender. The apothecia, or partial receptacles, 

 therefore, may be regarded merely as modifications of 

 the thallus itself, and as composed externally of the 

 same substance, though frequently of a different colour. 

 Upon making the section, certain vessels, disposed in 

 \ crtical rows, are displayed. These constitute the la- 

 mina proligera, or gfmmiparuus platr, (the seminal layer 

 I JjJSJirt, f Sprengel). They are compact, firm, smooth, and 

 | SfiJciBmi- pellucid. Within these, numerous small bodies are ob- 

 i*r .. served, which are the gougvli or bvd-knott already al- 



luded to, and whicR are minute opaque bodies. The 

 gelatinous substance of the gemmiparous plate being 

 Drought into a state of solution by continued moisture 

 during autumn and winter, the gongyli probably then 

 escape and germinate. In some lichens, the gongyli 

 are not produced in gemniiparous plates, but in gemmi- 

 parous nuclei ; and each nuclei!-. i~ invested with a 

 membrane called perilkfrium, which is horny when dry, 

 .UH I |*-llucid and gelatinous when wet. Both the plates 

 and the nuclei are divided into crlli, and often also into 

 renclri. Cells (the Ihrnr of Hedwig) are mere oblong 

 Teasels or cavitie*. If tbme only occur, the parenchy- 

 ma of the apothecium is said to be of timple tcjclure (si- 

 milart). The cells, however, nre frequently compound, 

 or contain within themselves smaller cells : these small- 

 er cells were erroneoii-ly considered ;i~ the naked seeds 

 by Hedwig ; but they Dare been ascertained to contain 

 li like the simple cells ; and are by Acharius 

 id by the name of veticlct. The cells of 

 are often found quite empty, though out- 

 wardly perfect ; yet gongyli abound in other parts of 

 the substance of the same apothecium. Gongyli are 

 universally to be found in lichens ; cells and vesicles, 

 however, are frequently wanting. The*e vessels are 

 apt to disappear through age. They dry up, too. like 

 other part* of the lichen, during hot weather ; and on 

 the return of the moist and cool season of the year, 

 they again expand ; characters, it may be noticed in 

 passing, which are quite inapplicable to seeds. 



If the apotbecia were to be considered as the fruit of 

 lichens, then one and the same species of plant must be 

 held as presenting often two, or even three different 

 kinds of fructification ; for some lichens, besides regu- 

 lar apothecia, contain tubercle-, -warts or pores, all 

 of which fumih the supposed seeds. The.ie, indeed, 

 are the parts which Hedwig regarded as the male or- 

 gan*, affording pollen ; they do not, however, fade and 

 disappear, after a short time, like the antherz and sta- 

 mina of flowers, but endure as long as the true apothe- 

 cia. They are termed cepliiilwlia by Acharius ; and he 

 mention*, that from the powder taken from some of 

 them, the lichen ha* been observed to be propagated. In 

 one gnat division of lichens, the apothecia may be said 

 to be fruit-shaped, and this might appear to strengthen 

 somewhat the arguiaent drawn from analogy ; but in 



two other great divisions, these organs are nowise fruit- Lichen, 

 shaped, but are of the nature and habit of the thallus """"Y"^ 

 itself. Even where no regular apothecia, or even no 

 powdery excrescences are to be seen, the gongyli or 

 bud-knots are not wanting ; for these are also distri- 

 buted through the frond or general substance of the 

 lichen. Some species of lichen, it is well known, very 

 rarely produce their shields pr apothecia; insomuch 

 that a specimen containing them is prized by botanists 

 as an invaluable treasure. This is the case, for example, 

 with Lichen nivalis and L. glauciis, (Cetrarise); L. 

 pustulatus, (Gyrophora) ; L. jubatus, (Alectoria) ; L. 

 pubescens, (Cornicularia) ; L. perlatus and L. physo- 

 des, (Parmelias) ; and with L. palmatus, (Collema) ; 

 perfect specimens of which form what Acharius would 

 call the " gazte of a lichenologist." It has often exci- 

 ted surprise, that plants which so seldom presented their 

 parts of fructification, should yet be abundantly spread 

 over our rocks and trees. This difficulty, however, is 

 now satisfactorily explained. These lichens, although 

 incomplete in the eyes of the botanical collector, are in 

 reality perfect plants of their kind, being enabled to 

 reproduce the ^pecies by means of the gems dispersed 

 in the substance of their fronds. 



It may here deserve notice, that, in this tribe of plants, Reproduc- 

 the reproduction by gems must be held as being as tion perfect, 

 complete and permanent as that by means of seeds. It 

 follows, that Mr. Knight's doctrine, " That the only 

 genuine reproduction in vegetable nature must be ef- 

 fected by seeds," cannot be considered as of universal 

 application, but will fall to be limited, at all events, to 

 phaenogamous plants. Perhaps it may be found to be 

 more particularly adapted to the arboreous plants with 

 which this ingenious writer is most conversant, and to 

 which it seems in every respect applicable. 



Lichens, therefore, according to the views of Acha- General 

 rius, may be described as forming a new peculiar Na- characters 

 tural Order, distinct from the other cryptogamia; and ' 

 as consisting of plants in which the whole body, whe- 

 ther frond or crust, performs the functions of a univer- 

 sal receptacle, or t/iallus; of various shapes ; without 

 a distinct root, or stem; perennial; furnished with 

 vegetative corpuscles or gongyli, (analogous to, but some- 

 thing intermediate between seeds and buds, though 

 most nearly allied to the latter), by which the species 

 is continued ; these gongyli abounding in every part 

 of the substance of the thallus, both externally and in- 

 ternally, either scattered, or collected in small nests, 

 and at the same time existing, inclosed in separate or 

 proper organs, which are sometimes fruit-shaped, and 

 generally coloured, called apolhecia or partial recep- 

 tacles. 



No account, it is believed, of the Acharian genera, 

 has hitherto appeared in any English publication. It 

 seems proper, therefore, not only to enumerate the ge- 

 neric names, but to detail the essential characters; and 

 the subject may probably be somewhat facilitated and 

 relieved, by mentioning a few of the more -remarkable 

 British lichens, as illustrative of the respective genera 

 of Acharius, under which they now fall to be arranged. 

 It may be noticed, that some years after the publica- 

 tion of his Prodramus Licheno^raphice Suecicce, and of 

 his Methodus Lichenum, Acharius gave to the world, in 

 1810, an enlarged and improved work, entitled, Li- 

 c/icnograpfiia Universalis, to the arrangement and no- 

 menclature of which we shall adhere. It might per- 

 haps be possible to dispense altogether with the terms 

 lhallus and apothecium, and merely to denominate the 

 former universal, and the latter partial receptacle; unless 



