Art. XU.—The Lichens of Victoria. Part I. 

 By Rev. F. R. M. Wilson. 



[Eead November 10, 1892.] 



INTRODUCTION. 



1.— Thk Structure ov Lichens. 



Lichens are cellular plants, and consist generally of 

 thallus, apothecla, and spermagones. 



1. The thallus is usuall}^ composed of layers (a) cortical, 

 (6) gonidial, (c) medullar^/, and (d) hypothaUine. 



(a) The cortical layer, which occurs on the upper surikce 

 of most, and also on the under surface of mau}^ lichens, 

 varies in composition, but is generally formed of closely 

 compacted cellules. It varies also in colour, in thickness, 

 in degree of tenacit}^ and in smoothness of surface. The 

 inferior cortex of many lichens is furnished with vhizincB, or 

 root-like filaments, by which the plants are attached to their 

 substratum. 



(6) The gonidial system, which generally occurs immedi- 

 ately under the cortex, is specially characteristic of this class 

 cf plants. When the gonidial cells are completely filled 

 with bluish or olive-green matter, they are called granula 

 gonlma; but when the yellowish-green contents are 

 suiTounded by a hj-aline .space within the cell, they are 

 called gonidia. Both kinds are usually sphteroidal. In 

 some genera the gonidia are flat and irregular in outline, 

 chroolepoid. Some lichens are chrysogonimic, with golden 

 yellow gonidia. 



(c) Tiie medulla, which is found beneath the gonidial 

 sj'stem of many lichens, consists of colourless, tubular, and 

 articulate filaments, more or less closely compacted or 

 interlaced. 



(d) The hypothallus, which is spread under the thallus of 

 some lichens, is usually (jf a dark colour, and is formed of 

 the filamentous growth arising from the germinated spores, 

 on which the other parts of the thallus are deposited. 



