296 



BOTANY. 



examples, while of the latter Usnea, Parmelia (Fig. 

 and Sticta (Fig. 201) may be taken as illustrations. 



Pig. 202. Parmelia aipolia. A, a. portion of a thallus with two apothecia, aj>, 

 and several spermagonia, , . 5, transverse section of thallus through an apothe- 

 cium ; cc, cortical layer of pseudo-parenchyma ; </, g', gonidial layers ; cm, medul- 

 lary layer ; h, h, hypothecium ; t, t, t, t, the hymenium ; th, asci (thecse), with 

 aacqspores. C", section through three spermagouia, s, , , rh, rh, rhizoids. D, 

 sterigmata from the interior of a spermagonium, bearing spermatia, ', '. After 

 Tnlasne. 



