3o6 LECIDINEI. PART n. 



a very peculiar structure, in strong contrast with that of 

 the Solorina crocea, which has veins on the under-surface 

 but no fibres, and as no rootlets are sent out from the 

 base of the disc, it remains superficial. M. Tulasne 

 discovered fertilizing particles in several species of this 

 group. 



The order of the Lecidinei contains numerous species 

 of the most varied habits. There is a distinct and regu- 

 lar series upwards in the genus Lecidea, the species of 

 which are always crustaceous, and often form merely 

 a thin, close, adherent fibrous stratum on the hardest 

 flint or quartz. Some of them disintegrate the hard 

 rocks on which they spread, possibly by the action of some 

 acid which they contain. From this low type, the genus 

 rises to the exalted forms with erect branching stems 

 clothed with foliaceous scales, and brightly coloured. 

 The order is distinguished by an orbicular disc, contained 

 in a distinct excipulum or cortical envelope, which is 

 open from the earliest age ; but it is frequently obliter- 

 ated afterwards by the development of that part of the 

 medullary stratum where the fruit is formed, the disc 

 in consequence becoming convex and capitate. This 

 transformation takes place in the highest forms of the 

 genus Lecidea. The genus Bseornyces has rose or chest- 

 nut coloured convex discs, supported on a stem called a 

 podetium. The genus Cladonia has a foliaceous thallus 

 producing free scale-like fronds, from the midst of 

 which spring cylindrical or cup-shaped podetia, which 

 are sprinkled with leaves. The margins of the cups or 

 tips of the branches bear an abundant crop of convex, 

 irregular brown, or deep red discs, often as brightly 

 coloured as sealing wax. 



The species of Lecidea bear severe cold, and are won- 

 derfully long lived. Mr. Berkeley mentions that there 

 are patches of the Lecidea geographica which probably 

 date from almost fabulous periods. 



