ASCOL1CHEXES. 



141 



constructed ascospores (Fig. 137), which are enclosed in asci 

 (Fig. 136), usually surrounded by paraphyses attached together. 

 Furthermore they possess pycnidia (Fig. 141) containing numerous 

 microconidia. These were formerly considered as organs of 

 fructification, and were termed " spermatia," and the pycnidia, 

 " spermogonia." Alfr. Moller proved, in 1887, that the micro- 

 conidia are able to germinate and produce a mycelium with new 

 conidia, just as in other Ascomycetes. 



VEGETATIVE REPRODUCTION takes place by soredia, which to the 

 naked eye appear as whitish powder on the surface of the thallus. 

 They are small round bodies, formed by one or a group of gonidia, 

 which are surrounded by a mass of felted hyphas. After the 

 rupture of the cortex they are set free, and readily carried by the 

 wind to other places, where under favourable circumstances they 



tablish a new thallus. 



FIG. 141. A A portion of the thallus of Parmelia pnrietina with ascocarps (a) and pycnidia 

 (I). B A portion of the thallus of Cetraria islandica with pycnidia at the end of small 

 lobes. C A lobe with pycnidia and ejected microconidia. (Magnified). 



GEOGRAPHICAL DISTRIBUTION. The Lichens are the most hardy 

 plants, and are the first to appear on hitherto bare rocks which 

 they gradually disintegrate, and hence prepare the way for the 

 growth of other plants. They are to be found from the Polar 

 regions to the Equator ; from the highest snow-free mountain- 

 peaks down to the level of the sea ; on the stems of trees ; on rocks, 

 soil, some even on inundated places ; on stones in woodland streams, 

 and on beaches ; but they are never found upon rotten organic 

 remains. Some grow gregariously in enormous masses, and form 

 wide-stretching carpets, e.g. Reindeer Moss (Cladonia rangiferina), 

 species of Cetraria and other fruticose Lichens. 



USES. On account of the cell-wall being composed of Lichen- 



