SOLORINA SACCATA. 29 



and in fresh and moist specimens is of a green colour, which, in 

 the herbarium, changes to grey or greyish-white. The margin is 

 divided by crenatures into lobes ; and the upper surface is thinly 

 covered with a white, granular dust, '' albo-granulato-pruinose," 

 Leighton. The under-surface is creamy white, and is furnished 

 with numerous prehensile, root-like fibres, termed rhizinse {^p'^la^ a 

 root), which serve simply to attach the thallus to its support. The 

 apothecia vary in colour, from light to dark brown ; when imma" 

 ture, they are small, and pressed closely to the upper surface of 

 the thallus, over which they are irregularly scattered. They 

 increase in dimensions as maturity approaches, at the same time 

 becoming urceolate, or concave and sunken ; hence the term 

 saccafa, from Latin saccus, a bag or sack. 



If a thin, vertical section be taken through the apothecium 

 and thallus, and examined with a magnifying power of three 

 hundred diameters, it will be found 



(i) That the thallus consists of three distinct layers, (Plate 5) : 

 (a) the cortical layer, formed of closely aggregated cellules, the 

 walls of which are more or less distorted, by mutual pressure, from 

 their original spherical shape ; {b) the stratum-gonidiale, consisting 

 of groups of orbicular granules, filled with a green-coloured matter; 

 {c) the medullary layer, formed of numerous intertwining filaments, 

 which branch dichotomously, and in appearance closely resemble 

 the mycelium of Fungi. [Two kinds of thallus structure occur, 

 termed respectively Heteromerous (erepog, different ; i^^pog, a part) 

 and Homoiomerous {o\ioioq^ similar ; fi£jOoc, a part, the characteristic 

 differences of which are generally well marked.) In the former class, 

 of which Soloriiia saccata is a type, the gonidia and the hyphas 

 occupy definite and distinct areas ; in the latter, these two kinds 

 of tissue are equally blended together in the formation of the 

 thallus.] 



(2) The spores, which are contained in asci (daKog, a wine-skin) 

 or hyaline envelopes, are reddish-brown, ellipsoid, thick-walled, 

 and divided across their centre by a septum ; and their epispore, or 

 outer wall, is marked by many granular dots or points. They 

 vary greatly in dimensions, in different specimens ; but in all they 

 appear to diminish in size towards the circumference of the apo- 

 thecium. According to Mudd, they measure 'ooS inch in length, 



