LICHENS. 



[ 465 ] 



LICHENS. 



and, 3, pycnidia, in which are developed 

 sti/lospores like those of Fungi. 



The commonest form of the apothccia is 

 that of sessile or stalked disks or cushions, 

 flat, convex, or hollowed into a cup (fig. 

 396) ; in other cases they are linear ; these 

 open forms characterize the formerly-called 

 Gymnocarpous Lichens. While in the 

 Angiocarpous genera the apothecia or rather 

 perithecia are closed globular receptacles or 

 conceptacles, analogous to those of the Sphce- 

 ri(B among the Fungi, and opening at the 

 summit to discharge the spores (fig. 39o). 

 The apothecium may he composed of two 

 parts — the tludamium or hymeninm, and the 

 excipulum. The excipulum, when present, 

 sometimes forms a cup-like envelope derived 

 from the thallus, and of the same colour 

 (thaUine), or it may differ in colour and 

 texture, in which case it is termed proper. 

 Or it may entirely or partly surround the 

 thalamium and theca?, and then forms the 

 peritheciiim. The t/iahi»tiio>i is represented 

 by the body of the apothecium, open or 

 closed; and the layer of its cells immediately 

 lining the bottom of the cup, shield, or 

 conceptacle is sometimes called the hypo- 

 thecium, which bears the thec(S and the 

 paraphyses (fig. 398) ; the latter are filiform 

 or clavate cells (PI. 37. figs. 6 & 12), pro- 

 bably abortive thecse, among which they 

 are intermingled ; both these and the thecse 

 stand perpendicularly upon the hypothe- 

 ciuni, being surrounded by a gelatinous sub- 

 stance — the gelatina hymenea. The thecce 

 (PI. 37. figs. 6 & 12) are usually ovoid or 

 elongated cells with thick walls, containing 

 the spores ; the thecse are shorter than the 

 paraphyses surrounding them ; and the 

 whole are usually glued firmly together by 

 their contiguous lateral surfaces. 



The spores consist of two layers, an epi- 

 spore and an endospore ; the former are tinged 

 blue with tincture of iodine, and present 

 many points of difference in different genera 

 and species. In Verrucaria muralis they 

 are ellipsoid, colourless, perfectly smooth 

 and semitrausparent, containing gi-anular 

 matter ; while in V. epidermidis and ato- 

 maria they are bilocular bodies, representing 

 a pair of obovoid cells adherent by their 

 thick ends. In their earlier stages of de- 

 velopment they appear solid ; subsequently 

 four nuclei or oily globules are seen in them, 

 each occupying a spherical cavity. The 

 membrane of the spore then becomes thin- 

 ner, and finally its two cavities coalesce into 

 one. When ripe, these spores are about 



1-1. "jOO" in length and about 1-4000" broad. 

 There are eight in eacii theca, and they are 

 separately enveloped in a mucilaginous coat. 

 The spores are largest in the genus Pertu- 

 sdria. Those of P. communis are visible to 

 the naked eye ; and observed in water soon 

 after emission from the thecse, they are not 

 less than 7-1000" to 8-1000" long by 5-1000" 

 broad. Their simple cavity is filled with 

 granular semitrausparent 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 Par^nelia 

 (Physcia) offers both simple and bilocular 

 spores. Of the former, P. purietina gives 

 an example, though in some cases a trans- 

 verse partition is formed, and this is the 

 normal state in P. stellaris (PI. 37. figs. 6 & 

 7). In Ptltigera (PI. 37. fig. 11) the spores 

 are elongated. In Collema and other genera 

 the spores are divided into fom- chambers 

 by three transverse septa. 



In several species of Lecanora, Lecidea, . 

 Urceolaria, &c., a more complex form of 

 spore exists, longitudinal together with 

 transverse septa dividing the cavity into 

 several series of chambers. Those of Urceo- 

 laria (PL 37. fig. 17) have eight or ten 

 compartments ; those of Lecidea urceolata, 

 Thelotrema lepadina, Umbilicaria pushdata 

 (PL 37. fig. 18), and other Lichens, called 

 muriform spores, have a much larger num- 

 ber of little cavities, each containing a 

 distinct nucleus. 



The emission of the ripe spores takes 

 place in the same way as in the Pezizce, 

 Hehellcp, Sph(eri<e, 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 apothe- 

 cium will be found covered with patches of 

 spores, easily perceptible by their colour, 

 these having been projected from the apo- 

 thecia 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 

 tlian 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, Peltiyera, Col- 

 lema, Borrera ciliaris, Verrucaria muralis, 



2h 



