384 



ORGANOGRAPHY. 



the number is always constant for each species. In rare cases 

 the thecas have a large number of spores, and are hence said to 

 be polysporous. The spores are sometimes termed sporidia or 

 sporules. Some of these spores are of a very complex structure, 

 being di^nded into two (Jfig. 821), four, or many cells. They 

 are frequently beautifully coloured, and form splendid objects 

 under the microscope. 



In two genera of Lichens, namely, in Ahrothallus and 

 Scutula, certain structures have been discovered by Tulasne, 

 called stylospores. These are analogous to the stylospores of 

 Coniomycetous Fungi. " They consist of isolated spores borne 

 upon shortish simple stalks. They are produced in concep- 

 tacles to which is applied the name of pycnidia." 



The spermagonia or spermatogonia were first discovered by 

 Tulasne, but they have been now found in a great number 

 of Lichens, and probably exist in all. They generally appear as 

 little black specks near the margins of the thallus, in the tissue 

 of which they are usually more or less imbedded {fig. 819, .«p) ; 

 rarely, they are quite free and above the thallus. The sperma- 

 gonium varies in form, and has one or more cavities, with a 

 small orifice at the top termed the ostiole or pore (^fig. 822, as), 

 with which all the cavities communicate. The spermagonium 



Fig. 823. 





Fig. ft22. Vertical section of 

 a Bpermai^onium of Clarlonia 

 rangiferiiui. gp. Spermato- 

 phores. os. Ostiole or pore, 

 from which the sperinatia, 

 », are escaping. After Jlen- 



frey ■/•"(>/. H2.!. Highly 



maijnifled fragment from the 



wall of a spermagonium of Parmelia parietina. 



phores. «. Spermatia. After llenfrey. 



when mature, has its interior filled with a number of bodies called 

 spermatia (^figs. 822, 5, and 823, s), raised on stalks, termed sper- 

 matophores \figa. 822, sp, and 823, sp). The form of the sperma- 



Articulated epermato- 



