LICHENS. 



[ 390 ] 



LICHENS. 



branched, filamentous, pseudo-radical pro- 

 cesses. 



Putting aside the gonidia or gemmule- 

 cells of the thallus, the reproductive organs 

 of the Lichens are of two kinds: 1. the 

 apothecia, which, according to their forms, 

 receive diiferent names, and are all charac- 

 terized by producing the sacs (thecce) con- 

 taining spores; and 2, the spermagonia, 

 which some regard as antheridia, and which 

 produce extremely minute cylindrical bodies 

 growing at the ends of short pedicels, from 

 which they are ultimately detached, like the 

 spores of many Fungi. 



The commonest form of the apothecia 

 is that of sessile or stalked disks or cushions, 

 flat, convex, or hollowed into a cup (fig. 401 ); 

 in other cases they are linear, and these 

 open forms characterize the division called 

 Gymnocarpous Lichens, while in the Angio- 

 carpous genera the apothecia are closed 

 globular receptacles or conceptacles, analo- 



fous to those of the Spharice among the 

 ungi, opening finally at the summit to dis- 

 charge the spores (fig. 399). The apothecia 

 are lined by a special layer of cellular tissue, 

 sometimes called the hypothecium, which 

 bears the thecce &n&ihe paraphyses (fig. 402); 

 the latter are filiform or clavate cells (PL 29. 

 figs. 6 & 12), probably abortive thecae, 

 among which they are intermingled; both 

 these and the thecae stand perpendicularly 

 upon the hypothecium. The thec<s (PL 29. 

 figs. 6 & 12) are usually ovoid or elongated 

 cells with thick walls, containing the spores ; 

 the thecae are shorter than the paraphyses 

 surrounding them, and the whole are usu- 

 ally glued firmly together by their contiguous 

 lateral surfaces, and the entire mass of thecae 

 and paraphyses is called the thalamium. 



The spores present many points of difference 

 in different genera and species. In Verru- 

 caria muralis they are ellipsoid, colourless, 

 perfectly smooth and semi-transparent, con- 

 taining granular matter ; while in V. epider- 

 midis and atomaria they are bilocular bo- 

 dies, representing a pair of obovoid cells 

 adherent by their thick ends. In their 

 earlier stages of development they appear 

 solid ; subsequently four nuclei or oily glo- 

 bules are seen in them, each occupying a 

 spherical cavity. The membrane of the 

 spore then becomes thinner, and finally its 

 two cavities coalesce into one. When ripe, 

 these spores are about 1-1500" in length 

 and about 1-4000" broad. There are 

 eight in each theca, and they are sepa- 

 rately enveloped in a mucilaginous coat. 



The spores are largest in the Angiocarpous 

 genus Pertusaria. Those of P. communis 

 are visible to the naked eye, and observed 

 in water soon after emission from the 

 thecae, they are not less than 7-1000" to 

 8-1000" long by 5-2000" broad. Their 

 simple cavity is filled with granular semi- 

 transparent matter, usually with oil-globules 

 of various sizes. The epispore is very broad, 

 transparent, and formed of several lamellae ; 

 these also are coated with mucus. The 

 genus Parmelia offers both simple and bilo- 

 cular spores. Of the former, P. parietina 

 gives an example, though in some cases a 

 transverse partition is formed, and this is 

 the normal state in P. stellaris (PL 29. figs. 

 6 & 7). In Peltigera (PL 29. fig. 11) the 

 spores are elongated. In Collema and other 

 genera, the spores are divided into four 

 chambers by three transverse septa. 



In several species of Lecanora, Lecidea, 

 Urceolaria, and a great number of Angio- 

 carpous Lichens, a more complex form of 

 spore exists, longitudinal together with trans- 

 verse septa dividing the cavity into several 

 series of chambers. Those of Urceolaria 

 (PL 29. fig. 17) have eight or ten compart- 

 ments ; those of Lecanactis urceolata, The- 

 lotrema lepadina, Umbilicaria pustulata (PL 

 29. fig. 18), and other Lichens (called muri- 

 form spores), have a much larger number of 

 little cavities, each containing a distinct 

 nucleus. 



The emission of the ripe spores takes 

 place in the same way as in the Pezizce, 

 Helvellts, Sphcerice, and many other Fungi 

 of the same kind. If a portion of the thallus, 

 moistened, is placed in a common phial, with 

 the apothecia turned toward one side, in about 

 eight or ten hours the surface of the glass 

 opposite each apothecium will be found co- 

 vered with patches of spores, easily perceptible 

 by their colour, these having been projected 

 from the apothecia with force. If placed on 

 a moist surface, and a slip of glass laid over 

 them, the latter will become covered with 

 them in the same way ; and Tulasne states 

 that they are projected to a distance of more 

 than half an inch from the theciferous layer, 

 the spores being emitted continuously for a 

 long time. The experiment may be tried 

 either in winter or summer, and has been 

 made with success on several common spe- 

 cies of Parmelia, Lecanora, Peltigera, Col- 

 lema, Borrera ciliaris, Verrucaria muralis, 

 Endocarpon hepaticum, Pertusaria, Urceo- 

 laria, Opegrapha, &c. 



Tulasne explains the elastic discharge of 



