THE FUNGI 



249 



-P 



At an earlier stage of development the apothecium is 

 closed, and consists of a mass of hyphre surrounded by a 

 cortical layer. The paraphyses which arise from the 

 hypothecium are the first elements of the hymenium to 

 be developed. The asci, which in many cases have been 

 observed to arise from the 

 branches of a distinct hypha, 

 differing from those which 

 produce the paraphyses, are 

 developed relatively late. They 

 grow up among the paraphyses, 

 insinuating themselves between 

 them until they attain an equal 

 height. At the same time the 

 envelope of the fruit is opened 

 at the apex, and the edges 

 gradually pushed back as the 

 hymenium expands. 



The development of the 

 apothecium may go on for a 

 very long time, even for years 

 in some cases, new asci arising 

 towards the exterior margin. 

 Each ascus at a certain stage 

 of development contains in its 

 protoplasm a single nucleus, 

 which subsequently undergoes 

 repeated division, into two, 

 four, and eight. When the full number is attained, a 

 cell is formed around each nucleus, and these cells 

 become the eight ascospores. The contents of the ascus 

 are not, however, completely used up in the process of 

 spore - formation ; a certain part remains over, lying 



FIG. IQl.Physciaparietina-, 

 part of a vertical section 

 through an apothecium. p, 

 paraphyses ; a, asci one 

 immature, the other two 

 containing eight ascospores 

 (sp) each ; c (above), hypo- 

 thecium ; A, A, layers of 

 algal cells ; m, medullary 

 layer ; c (below), the lower 

 cortical layer. Magnified 

 about 250. (After Lauder 

 Lindsay.) 



