LICHENES. 



645 



cortical or outer layer, it expands in the form of shield-like discs, called 

 apothecia (amSrixii), a repository), or patellae (figs. 891 s, 892 a), (patella, 

 a hollow disk), or linear expansions called lireUse (lira, a furrow). 

 Sometimes the cortical matter forms a border round the fructification. 



^,:/' 



Kg. 891. 



Fig. 893. 



at other times it grows up in the form of a stalk, so as to give rise to 

 a podetium (toDs, a foot). The young thecee (asei) contain spores, 

 varying from 4 to 8 (fig. 449, p. 251), or from 12 to 16. Occasion- 

 ally the spores are in sets of two (fig. 449, 2, p. 251). Separated 

 cells of the medullary layer, of a green colour, called gonidia (yovn, 

 generation, and eldog, resemblance), or gongyli, are considered as 

 another kind of reproductive organ. There are also capsular bodies 

 called spermogones, containing minute linear cells or spermatia, which 

 are often supported on stalks or sterigmata (fig. 475, p. 268). 

 Besides these, pycnides (fig. 476, p. 268), or bodies like spermogones 

 occur, containing spore-like cells, called stylospores (figs. 473, 474, 

 p. 268). Lichens bearing fructification in cavities of the thallus, and 

 opening by a pore on the surface, are called angiocarpous, while those 

 which have the fructification expanded in the form of a shield-like 

 scutellate, cup-shaped, or linear thallus, are called gymnocarpous. 

 The order has been 'divided into four sections : — 



1. Hymenothalame» (ipt^v, a memtirane, BdXSiios, a receptacle) : shields open, " 

 discoid, permanent, nucleus bearing the sporangia on its surface (fig. 891). 



Figs. S91-893. Organs of fructifleation of Parmelia Acetabulum, to illustrate the natural 

 ■order Lichenes, section Hymenothalamese. Fig. 891. t, Thallus of the Lichen, s, Apo- 

 thecia in the form of shields in different degrees of development. Fig. 892. Apotheoium, 

 •a, out vertically and magnified in order to show the layer, tp, foimed by the union of theese 

 and paraphyses. Fig. 893. A small portion of the apothecium much more magnified, 

 Showing, cm, the central meduUaiy layer, m. The cortical layer, t i, Theese in different 

 degrees of development p, 



