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matured ; and in this family they are not ejected to the exterior be- 

 cause of the closed perithecium and exciple, but are retained in the 

 space above the thecium, where they mature ; later, the perithecium 

 opens by an apical chink or pore, thus allowing the spores to escape. 



A very simple experiment will illustrate the forcible ejection of 

 spores. By placing fresh spore-bearing lichens in a moist chamber 

 and laying a cover-glass over the apothecia it will be found in a few 

 hours that the cover-glass contains numerous spores which have been 

 propelled against it. Tulasne and Ohlert have estimated that the 

 spores may be projected to a distance of more than two centimetres. 

 On examining the slip bearing the ejected spores it is found that 

 they occur in groups in which the prevailing number is eight, as the 

 majority of spore-sacs bear eight spores ; this grouping is due to the 

 fact that the spores are held together by a gelatinous substance 

 which compels them to escape at the same time. This gelatinous 

 substance is especially apparent in spore-sacs bearing numerous 

 spores, as Biatorella and related genera ; sometimes the exosporium 

 is very gelatinous and swells enormously when moisture is added ; 

 this no doubt serves the purpose of aiding in their expulsion as well 

 as in enabling them to adhere to any suitable substratum. 



The spores of the entire apothecium are by no means all ejected 

 at the same time, dissemination continuing for a long period under 

 favorable conditions, as during showers, damp weather, or dews. 

 Neither are the spores of one and the same apothecium all matured 

 at the same time ; for an examination of sections of various apothecia 

 shows mature spore-sacs associated with others just beginning to form ; 

 this, in a measure, explains the long period of spore-ejection. 



While the spores are ejected during moist periods their distribu- 

 tion takes place mainly during dry periods. On ejection the spores 

 either fall back upon the disk of the apothecium or in its immediate 

 vicinity, especially upon the surface of the thallus. During periods 

 of dryness they lose much of their moisture, the gelatinous substance 

 shrinks and becomes hard, and the entire spore-substance becomes 

 lighter, thus enabling air-currents to distribute them more readily. 



From the comparatively insignificant part that spores play in the 

 process of reproduction it is not reasonable to suppose that there are 

 many structural adaptations favoring their distribution. All the ex- 

 tensive phylogenetic adaptations in the apothecium are primarily in 

 favor of an increase in the function of assimilation ; such are the 



