68 



POPULAR HISTORY OF LICHENS. 



thecge is sent forth by the hypotheciuin during the life of 

 the apothecium, which, like the thallus, is perennial. 



The Spore (airopa, a seed) varies greatly in form, size, 

 and colour. Its form is usually ovoid or ellipsoid ; some- 

 times fusiform, elongated, or linear. It is either simple, 

 consisting of a single cell; or compound, formed of, or 

 containing, two or more smaller cellules arranged in definite 

 series, and usually separated by distinct intervals or septa, 

 or dissimilar in size, and aggregated in a confused manner, 

 constituting what are termed cellular spores. The one-celled 

 or simple spore is usually simple also in shape ; the com- 

 pound spore, on the other hand, presents great irregularity. 

 When the spore consists of two large cells in apposition 

 by one surface, it assumes somewhat of the appearance of 

 the figure 8, modified by pressure ; where there is a greater 

 number of constituent or contained cells, the spore-wall 

 presents a series, regular or irregular, of bulgings. In one 

 species, the common Pertusaria communis of our trees, the 

 spores are so large when isolated and spread on a slip of 

 glass, as to be, on careful examination, visible to the naked 

 eye; in other common species, such as the Cladonias, on 

 the other hand, they are so small as to require high powers 

 of the microscope for their discrimination; between these 



