LICHENS. 31 



minute and inconspicuous tubercular bodies on the surface of the 

 thallus, hned internally with the cylindrical, straight, or curved 

 spermatia, whose office it is to fertiUse the spores. The apo- 

 thecia, on the other hand, are easily detected by the eye in 

 most cases. A common yellow Lichen, forming circular patches 

 on most of our walls, is seen to be studded with reddish shields 

 or targets, the apothecia of the plant, containing numerous 

 colourless, pear-shaped vessels, which in their turn enclose the 

 spores. These cases, known as asci or thecae, are surrounded by 

 filaments called paraphyses, which are welded together more or 

 less firmly by a gelatinous substance, and which serve to protect 

 the thecae. 



The appearance which the apothecia present differs widely in 

 different genera, though the internal structure is much the same in 

 all, and amongst our own Lichens we may easily collect types of 

 the principal variations. The shield-like form, to which I have 

 alluded, is common. Again, certain apothecia resemble shallow 

 cavities, or cups, sunk in the substance of the thallus. In the 

 large genus Verj-ucaria, the apothecium is entirely covered by an 

 integument known as the perithecium^ which gives it a remarkably 

 convex appearance, and eventually opens by a pore, through which 

 the spores escape. The genus Pertiisaria^ common on trees 

 about us, is in reality one of the most abundantly fertile of our 

 British genera, and has spores of enormous dimensions, com- 

 paratively speaking; — but the apothecia might easily be passed 

 over, and the Lichen regarded as sterile, owing to the fact that 

 tubercles composed of thalline substance almost completely 

 envelope them. But by far the most remarkable fructification is 

 that of the GrapJiidece. A close observer of the tree-trunks in 

 our beech-woods will have noticed pale spots on the bark, 

 definitely bounded by darker lines, upon which are traced most 

 singular markings, which can forcibly be compared to the letters 

 of the alphabet of some Oriental language. These weird and 

 mysterious-looking characters are in reality the apothecia of the 

 genera Graphis and Opegrapha — sometimes simple, often con- 

 fluent, branched, and radiate, and always much elongated. 

 Such specific names, as Graphis scripta (the Lichen scripiiis of 

 Linnaeus) and Graphis sophistica, reproduce the impression 

 conveyed by these curious forms. 



Lastly, I may mention the odd little stalked fructification of 

 the genus Calicium, which is very fungoid in appearance and 

 structure. The thecce, or spore cases, are usually pear-shaped or 

 flagon-shaped ; but the spores themselves vary considerably in 

 shape, size, structure, colour, and number : the number in each 

 theca being, however, almost constantly the same in each 

 individual of a species. They may be egg-shaped, elliptic, 



