310 VERRUCARIEI. PART n. 



closed sporidia, there is a nucleus in each disc, either 

 of firm or deliquescent matter. 



Some of the lichens of this group are parasitic, others 

 are aquatic. The order Limboriei, like parasitic fungi, 

 begin their existence under the thick skin of the leaves 

 of tropical plants, spread their crustaceous thallus over 

 their surface, and destroy their beauty, by stopping 

 up their pores, and preventing the admission of light 

 to their tissues. The excipulum and perithecia are 

 black, and the latter burst in an irregular fissure, and 

 are in most cases covered by a beautifully sculptured 

 crust. 



The crustaceous fronds of the Yerrucariei are often 

 so thin as to be inseparable from the substance over 

 which they spread. The excipula are closed, the walls 

 of the perithecia are often black, and in some species 

 more or less crowded round a columella, In the 

 Yerrucaria muralis fertilizing particles have been dis- 

 covered. The plants are widely distributed, and at least 

 one species spreads its crust over the smooth stones in 

 running streams. 



In the group Endocarpei, the perithecia are immersed 

 in the substance of the plant, which has, for the most 

 part, a foliaceous horizontal crust, and a gelatinous 

 nucleus. Some species grow on stones, perpetually 

 or periodically submerged, or, if not under water, con- 

 tinually wet with its spray. The Lichina, a genus 

 of the group Lichinei, lives on marine rocks, and 

 is often dripping with salt-water, and often suddenly 

 dried up. 



The Sphserophorei, or sphere -bearing lichens, have 

 upright stems bearing globular fruit at the extremity of 

 their numerous branches. At first, the fruit is only 

 indicated by a swelling, but in time the outer bark bursts, 

 and exposes the contents of the perithecium, which 

 consist of asci and paraphyses seated on a central 



