VEGE TA 77 1 E RETROD UCTION. 



225 



as homologous with a hair. Sometimes the sporangia, 

 although really free, are overgrown by adjacent parts, so that 



Kig. 225.— A lichen {Parmelia conspersa) growing on a stone, showing the leaf-like 

 thallus (.mycelium 1 , with many fructifications lapothecia 1 . The older ones are more 

 or less irregular and large with a narrow rim ; the younger are nearer the margin, cir- 

 cular, and nearly closed over at top. Natural size. — After Frank. 



Fig. 226.— A vertical section of an apothet ium ol a li( hen 1 , \ naptychia ciliaris). h, 

 the hymenium; y, the subhymeruum, a layer. .1 densely interwoven hyphae; .-. r, the 

 sterile' hyphae which partially enclose the hymenium ; rn, the loosely woven hyphae <>t 

 the thallus; a, the algae enslaved by the fungus, Magnified about 50 diam.— After 



Sachs. 



they are enclosed in a chamber, whence the spores est apt- 

 after they are set free by the bursting of the sporangium. 



