36o LI CHINES [chap. 



of the Lichen, — the green cells still retaining their vitality 

 being set free on the disintegration of the crust. Recent 

 observations however show that the "gonidia" alone 

 cannot reproduce the Lichen, but merely their like; that 

 they give origin to other similar cells, but nothing more, 

 and that they present precisely the characters of the lower 

 groups of Algse, to various genera of which Order they may 

 be actually referred. Intermingled with the germ-cells and 

 in intimate contact with them, as well as usually forming 

 alone the stratum of the crust immediately beneath that 

 in which the gonidia abound, are long irregularly ramified 

 thread-like cells, destitute of chlorophyll, matted often 

 densely together, forming the mass of the crust. From 

 the cortical cells of the lower surface copious root-like 

 hairs are given off which serve as holdfasts to the thallus. 



Upon the upper surface of the crust and usually visible 

 to the naked eye, occurs the so-called " fructification," 

 although the asexual origin, in the form of convex, flat, or 

 saucer-Hke disks in some Lichens {GymnocarpoMS or dis- 

 ciferous genera), or in others as rounded cavities embedded 

 in the substance of the crust, opening at the surface merely 

 by a minute aperture {Angiocarpous or nucleiferous genera). 

 These disks or cavities are lined closely with erect, narrow, 

 often calvate, densely packed, microscopic cells, amongst 

 which are numerous asci, each containing usually eight or 

 fewer spores, originating, as in ascomycetous Fungi, by 

 free-cell formation. These spore-containing asci originate 

 from, and in direct continuity with, the colourless filaments 

 which form the mass of the Lichen, and are not in any 

 organic relation with the gonidia. 



The spores are liberated in damp weather, and on germina- 

 tion develop thread-Hke filaments similar to those which, 

 matted together, form the tissue from which the asci originates. 



