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Special Morphology and Classification. 289 
eight spores formed simultaneously. When the same thallus 
. bears both apothecia and svermogonia, the ‘Lichen is said 
to be moncecious ; when these organs are found on different 
‘individuals, it is dicecious. No true process of impregna- 
tion has yet been observed. 
Lichens possess a peculiar double nature. Their 
gonidia contain chlorophyll, and are algoid bodies; and 
their presence is the only certain distinction between. 
Lichens and Fungi; the Ascomycetes among the latter hav- 
ing an especially close relationship to the Lichens through 
their apothecia. In only a few cases have the gonidia been 
detached from the thallus and made to develope inde- 
pendently, by the formation chiefly of swarmspores. From 
this fact the theory has originated that Lichens are ascomy- 
cetous Fungi which are parasitic on particular Algze, the 
Pic. 414.—Cladonia digitata, a Fic. 415.—Cetrarta islandica, a Fruticose 
Fruticose Lichen ; @ apothecia ; Lichen; the margin of the thallus is 
4 cup; ¢ foliaceous thallus (natu- fringed, and bears spermogonia on the ~ 
ral size). edge of the fringe ; there are no apothecia, 
gonidia. This theory has been confirmed by the produc- 
tion of a perfect Lichen, Collema glaucescens, by sowing its 
U 
