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Special M orphology and Classification. 285 
’ 
Crass) ERT... ° Lechenese 
Lichens (Figs. 409-417) usually consist, when mature, of 
a well-developed layer of tissue, the ¢Hadlus, composed, 
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Fic. 409.—Usnea barbata: I. natural size with the spoon-shaped apothecia ; II. 
longitudinal section through the middle of the apex of the thallus ; the cortex, the 
gonidial layer g, and the medulla are clearly distinguishable (x 515); IIl.a 
single gonidium (Xx 700); IV. development of the soredia, a gonidial group of 
eight cells ; 6a similar group in a more advanced stage of development ; ¢ longi- 
tudinal section of amature soredium ; d the same with the gonidia more distinctly . 
separated ; ¢ a germinating soredium ; / the same further developed (X 500-700), 
