55 



top of the theca. The outer tangential walls become 

 strongly thickened and the inner ones in a less 

 degree. The transverse walls are partially thickened. 

 When the annulus and operculum are thrown off, 

 all the remaining tissue, with the exception of the 

 thickened walls, shrivel up, and the spores fill up 

 the theca. The peristome thus consists of two con- 

 centric circles, the outer being termed teeth, and the 

 inner cilia. The teeth and cilia are hygrospopic in 

 a different degree. 



ALTERNATION OF GENERATIONS. 



Spore produces Protonema. j O h f 



Protonema produces Moss Plants. > ^ "f • 



Moss Plants produce feexual Organs. ) 



Sexual Organs produce Sporogoniuua. \ Sporophyte 

 Sporogonium produces Spores. | Generation. 



The alternation of generations in the MuscinecB is 

 the converse to that exhibited in the Vascular 

 Cryptogams. The Sporophyte is parasitic upon the 

 Oophyte Generation. 



G^V^(^^%^y:^K^ 



