FUNGI.— LICHENS. 



123 



ascus in Bactrospora, Acnrospora, and Sarcogyne. The spores show a considerable 

 variety of structure, though this is similar in general to that of the Ascomycetes ; 

 they are often septate and muUicellular, like those of many Pyrcnomycetes ; the 

 exosporium is usually smooth and often variously coloured. 



The spores are set at liberty when water finds its way to the hymenium ; they are 

 suspended in the fluid which fills the ascus and are discharged with it when the ascus 

 bursts at its apex ; the discharge is probably the effect of the swelling of the para- 

 physes, and of the capacity for swelling possessed by the wall of the ascus itself. 



The germination of the spores consists in the development of a hyphal filament 

 from the endosporium of each cell of a spore ; the filament branches and spreads over 

 its moist substratum. The germination of the very large spores of a few genera, 

 Megalospora, Ochrolechia, and Pertusaria, is peculiar ; the spores are unicellular and 

 filled with drops of oil (Fig. 82, A, B), and each may put out as many as a hundred 



riG. 82. Lichen-spores g-erminating. A optical longitudinal section of spore of Pot 

 after lying thirty-four hours in glycerine ; s first beginnings of the germ-tubes. II P^rtuscJiia Ujoflaca, spore 

 H ith numerous germ-tubes, after de Bary, niagn. 390 thnes. C germinating septate spores of Soiorina sttccata. 

 After Tulasne, 



germ-tubes from different points in its circumference. The formation of each tube 

 begins with the appearance of a canal in the endosporium, which enlarges from 

 within outwards ; the protoplasm passes into it and becomes invested with a very 

 delicate membrane, which then grows in the outward direction in the form of a tube 

 (Fig. 83, A, B). 



Besides their spores Lichens possess organs named scrcdia, which assist materially 

 in their multiplication. The soredia are single gonidial cells or groups of gonidia, 



