730 



L 1C H Ek 



Lichen, and gelatine. (2.) Tlie other constituent part of the 

 '""V"' thallus, inclosed by the cortical, is called the medullary 

 substance. It is generally soft, cottony, or fibrous, and 

 apparently vascular. 



No spiral vessels are observable, nor have any parti- 

 cular kind of circulating vessels been traced in lichens. 

 Seldom, indeed, can the structure be shewn, to be either 

 distinctly vascular or cellular. 



Lichens, go simple in general structure, possess in a 

 strong degree that quality of the living principle, which 

 tends to the formation of new parts, or to the supply 

 of such as may have been injured. If a part of the 

 cuticle of a coriaceous lichen be destroyed, so as to 

 expose the internal white substance, this white part 

 soon acquires a greenish colour, which Ramond traced 

 to the extravasation of a peculiar juice. The different 

 parts of lichens often grow ' together, or become con- 

 joined, and the plants thus assume very various forms. 

 Indeed, the more simple the organization, the greater 

 seems the tendency to irregular sprouting ; and the 

 greater, of course, the dissimilarity between indivi- 

 duals of the same species. 



Lichens are not only perennial plants, but they pos- 

 sess the curious faculty of continuing for years, without 

 undergoing any perceptible change. Dr. Withering men- 

 tions one case, in which the parts of fructification of an 

 individual lichen remained, without visible alteration, for 

 the long period of ten years ! In such kind of fructifi- 

 cation we may confidently expect something very dif- 

 ferent, in nature and properties, from the flowers and 

 seeds of phasnogamous plants ; and it will soon appear 

 that we do meet with something very different. 



Fructification of Lichens. 



Fructifica- The fructification of lichens, or the mode in which 

 tion of they are propagated, has long been a botanical pro- 

 lichens, blem, which has exercised the talents, and divided the 

 opinions of the most acute cryptogamists. Before stat- 

 ing the doctrine of A charms, therefore, it may be pro- 

 per to advert to what was taught by Hedwig, and by 

 Gaertner, as the two most distinguished writers on the 

 subject. 



Hedwig. Hedwig, it is well known, bestowed much pains in 



examining the fructification, not only of the frondose 

 mosses, but of lichens ; and, till of late, his authority 

 was pretty generally assented to by botanists. On the 

 fronds of many lichens, numerous small mealy tubercles, 

 or wart-like excrescences appear, commonly of the same 

 colour and texture as the frond. On dividing, by a 

 vertical section, some of these tubercles in an early 

 stage of then- growth, Hedwig found them to consist 

 of a congeries of cells, each of them containing a gra- 

 nulous mass. The granules he regarded as particles of 

 pollen. When the tubercle acquires a deep brown co- 

 lour, it is at maturity ; the pollen then escapes, and 

 the tubercle becomes black. Here, therefore, we have 

 something like a male flower, especially in the eyes of 

 one bent on extending the sexual hypothesis to plants 

 of every tribe. On a different part of the same plant, 

 or on a different plant of the same species, appear a 

 number of cup-shaped or target-shaped bodies, either 

 .sessile, or supported on short pedicles, commonly of a 

 greenish colour, but gradually becoming dark as they 

 ripen. When the ripe cups and shields are divided by 

 a vertical section, they are found to contain, immedi- 

 ately under the dark crust at the top, a number of 

 small egg-shaped bodies, arranged in perpendicular 

 layers. These Hedwig considered to be the sporce, or 



seeds ; and the cups or shields were of course the fc- Lichen, 

 male flowers. - S "^"Y~'~ * 



The diligent and sagacious Gaertner took a different Gaertnct. 

 view. His observations led him to conclude, fliat the 

 powdery matter, and minute oblong bodies, contained 

 within the tubercles, shields, or saucers, consist not of 

 pollen or of seeds, but of a peculiar sort of gems or buds. 

 This kind of bud he denominates the proptigo, and de- 

 scribes as being a simple gem, without leaves or regular 

 shape, in some cases naked, and in others covered with 

 an envelope. When at maturity, these gems separate 

 from the parent plant ; they are dispersed in the same 

 way as seeds, and a new progeny springs up. They are 

 so far analogous to seeds ; but, considered physiological- 

 ly, they are more strictly allied to buds. 



It may here be remarked, that several of the more 

 perfect plants are bulbiferous ; as may be seen in the 

 true Lilium bulbiferum of Linnaeus, and the tiger-spot- 

 ted lily of China, L. tigrinum ; and in not a few of the 

 alliaceous tribe, such as Allium carinatum, and arena- 

 rium, which are both natives of Britain: viviparous 

 grasses are common on our upland pastures, as Aira 

 caespitosa vivipara, Festuca vivipara, and Poa flexuosa 

 and alpina : and many plants can be propagated by tub- 

 ers, as the common potatoe, and the Jerusalem artichoke. 

 All such plants, it will be observed, might, in favour- 

 able situations, produce seeds ; and if it be true, that 

 nature has provided these resources in order that the 

 species might with more certainty be continued in in- 

 clement regions, or on sterile soils, we might natu- 

 rally expect that lichens would, in that respect, be ad- 

 apted to the contingencies to which they are exposed, 

 of being successively scorched, drenched, and frozen on 

 the same barren rocks. It may be added, that the very 

 simple organization of the lichens might lead us a priori 

 to expect, that they would be increased by means less 

 complicated than are observed in phsenogamous plants. 

 It is justly remarked by Sprengel, that the propagation 

 by gems, in the less perfect plants, prevails more and 

 more as the organization is lower. It begins to occur 

 in the ferns, is more general in the mosses, still more 

 so in the hepaticae, and most prevalent of all in the li- 

 chens and confervas. 



The opinion of Gaertner has been established by the Lichens pro. 

 labours of Acharius ; and lichens (and probably also '"" buds. 

 Fuci, or sea- weeds) are henceforth to be considered as not sceds - 

 gemmiparous plants, propagated only by bud-knots, or 

 gongyli. 



It is remarked by Acharius, that the frond, which 

 constitutes the body of the lichen, performs the func- 

 tions of a universal receptacle, and may be regarded in 

 that light. The numerous processes already alluded to 

 as generally observable on the surface of the thallus, 

 and which, according to their shape and appearance, 

 have been called saucers, shields, and targets, are con- 

 sidered as finrt al receptaclrs, and are by him denomi- 

 nated Apoihecin. They are either regular or accessory. Apothccia, 

 When they occur of similar structure in various species or shields. 

 of lichens, and constitute a generic character, they are 

 said to be regular or true ; when they are variable or 

 irregular, and afford only specific distinctions, they are 

 said to be accessory. From the thallus, in many spe- 

 cies, rises a kind of little sfcilk, called podelin, support- 

 ing the apothecium. When the stalk is very small and 

 shortj it is styled podicella. The propriety of employ- 

 ing such new terms is obvious ; a peduncle, for example, 

 (the parallel term employed in speaking of phaenoga- 

 raous plants,) sustains the flower and fruit, and springs 

 from the stem; while the apotbecia of lichens present 



