208 



POPULAR HISTORY OF LICHENS. 



ends of the spore, — from, the endospores or membrane of the 

 cavities which contain the nuclear masses ; they are usually 

 dilated at their origin, but almost immediately bifurcate, 

 elongate, and ramify. In proportion as this filament grows 

 the protoplasm of the spore decreases, while its cavity in- 

 creases, the deposits of the epispore gradually disappearing, 

 like the albumen of a cotyledon, for the nourishment of the 

 young germ. Other spores having a small supply of pro- 

 toplasm also possess a thick epispore, whose thickened de- 

 posits are absorbed in proportion to the growth of the germ- 

 filament; while on the other hand it frequently happens 

 that spores rich in protoplasm have very thin walls, as in 

 Lecanora pallescens, var. joarella. The spermogones of P. 

 parietina are small tubercles scattered or grouped towards 

 the periphery of the thallus ; their sterigmata are short, ra- 

 mose, very irregular filaments, composed of delicate cubical 

 cellules, which afterwards become nearly solid from thicken- 

 ing deposit on the interior of their walls. The spermatia are 

 small and straight, and mixed with an abundant mucilage ; 

 they are developed laterally from the sterigmata, or from the 

 upper and outer surface of their constituent cellules. 



Chemical analysis has detected in this Lichen yellow and 

 red colouring matters, — the former being parietinic or chry- 



