1881.] 



MICKOSCOPICAL JOUENAL. 



203 



They sometimes require a lens to dis- 

 cover them ; but, on some thalloidal 

 forms they are plain and prominent. 

 As, for instance, the lacinise, of 

 certain Ramalinas, and the fronds of 

 Ricasolia attiplissima. The interior 

 of the spermogonic cell is composed 

 of a number of delicate, elongated 

 filaments, ;dl growing from the walls 

 of the vesicle, and at once project- 

 ing and converging into the centre of 

 it. These filaments are denomina- 

 ted sterigmata (Gr. sterigma, a prop 

 or support) from the fact that they 

 bear the spermatia. The sterigmata 

 are sometimes simple or articulate 

 and branched, and they bear the 

 spermatia on their sides or apices. 

 The contents of the spermogones, like 

 those of the apothecia, are truly li- 

 chenose, being filled and bathed with 

 lichenine. Perhaps, we should men- 

 tion another minute organ found 

 upon the Lichen, and named pycni- 

 des. These externally resemble sper- 

 mogones, and only a microscopical 

 examination can distinguish them. 

 They differ, however, in their internal 

 growth. Instead of sterigmatic fila- 

 ments, they contain simple, short, 

 thickish stalks, or stoutish cells, cal- 

 led basidia, which generate and bear 

 on their apices stylospores. These are 

 pyriform or oval bodies, something 

 like ordinary spores. The function 

 of pycnides, like that of spermogones, 

 is still very much shrouded in mys- 

 tery, and until this is understood, we 

 cannot truly know the real difference 

 between them. They are illustrated 

 by Fig. 48. 



We have already hinted that the 

 Lichen has no axis and no root. 

 Therefore it does not nourish itself 

 from the soil, or place, of growth. It 

 is an aerial plant, and what the water 

 with its solutions is to the Alga, 

 the damp atmosphere is to the Li- 

 chen. The whole plant imbibes nou- 

 rishment alike, and its growth is, 

 therefore, much affected by the puri- 

 ty, dryness, or humidity of the air. A 

 polluted atmosphere is destructive to 

 Lichen growth, while a flourishing 

 condition of these plants, is a sure in- 

 dication of the purity of the sur- 

 rounding aerial medium. On account 

 of their spongy, cellular nature. Li- 

 chens are strongly hygrometric. 

 After being in the herbarium for 

 years, on the application of moisture 

 which they greedily absorb, they will 

 freshen up and appear almost as 

 bright and green as when first gather- 

 ed. While humidity promotes their 

 growth yet they are capable of en- 

 during great drought. The crusta- 

 ceous Lichens are of very slow, and 

 frequently very long, growth. Some 

 are said to grow for hundreds of years. 

 They cover, and emboss in grey and 

 gold, the rocks on our highest moun- 

 tains ; to which they cling so closely, 

 that no storm affects them. The fo- 

 liaceous plants, contrary to the crust- 

 forms, attain their highest develop- 

 ment at low altitudes, and in shaded 

 places. Some of the softer and less 

 thalline plants grow to maturity in a 

 short space of time. I gathered my- 

 self, Odontotrema longius (Nyl.), in 

 considerable quantity on an old rail, 

 near Asby, Cumberland, in the au- 

 tumn of 1879. In the same month of 

 last year (1880), I visited the same 

 spot, and upon the old cuttings of the 

 previous year, upon the very knife 

 marks, I found the same plants re- 

 grown. No thallus was visible, but 

 some of the apothecia, when exami- 

 ned under the microscope, were fully 

 developed. This growth of the Li- 

 chen had been made in one year. 



The habitats of Lichens are almost 

 all objects on the surface of the earth. 



