90 A Short Talk on Lichens. [Sess. 



The lichen as a plant has no axis either ascending or de- 

 scending, no branches nor leaves as in phanerogams. It is 

 altogether an aerial plant, finding for itself a situs and then 

 deriving nourishment from the atmosphere. It can scarcely 

 be doubted, however, that mineral matters are to a very slight 

 extent absorbed from the soil or from their bases of support 

 and contribute to the colour of the thallus. Lichens are 

 light-loving plants, but appear to shun the direct rays of the 

 sun. Starch, gum, oil, sugar, resin, &c., as well as many 

 mineral substances, have been found in lichens. Their life is 

 twofold — active and passive — growing when supplied with 

 moisture, and resting when the atmosphere is dry, and this 

 accounts in a great measure for their almost indefinite duration 

 of existence, for some are hundreds of years old. The lichenine 

 which they contain is readily dried and as readily moistened. 

 This lichenine is a special kind of gelatin peculiar to lichens, 

 and is intermediate between dextrin and starch and readily 

 imbibes water. Cladoniai, for instance, if kept dry for years, 

 can be revived by sprinkling them with water or even by ex- 

 posing them to the atmosphere. 



The vegetative or growing portion of lichens is the thallus, 

 which may be said to comprehend the whole plant — root, stem, 

 and leaves — in one, and also because it contains within its 

 tissues or bears upon its surface the reproductive organs with 

 the fruit. The reproductive organs are the apothecia or 

 female organs, spermogones, the presumed male organs, and 

 pycnides, a secondary kind of fructification. The apothecia 

 as well as the thallus and the spores are all variable either in 

 form, size, colour, consistence, or internal structure. As a 

 rule, lichens are more or less of a spherical mode of growth, 

 and this is the form of greatest security, because it possesses 

 the property of greatest symmetry in relation to all its parts. 

 The thallus may be vertical or horizontal. When vertical, it 

 may be fruticulose, as in Cladonise and Eamalina ; or 

 filamentous, as in Usneae and Alectoria. Usnese, when full 

 grown, are perhaps the most beautiful of lichens ; their colours 

 are often brilliant, their habit elegant, and in fruit very strik- 

 ing. When the thallus is horizontal it may be crustaceous, as 

 in Lecanora ; or foliaceous, as in Parmelia and Sticta. Among 

 the Parmeliacei occur the highest forms of which lichens are 



