TIIALLOPHYTES : FUNGI 



79 



plant. In other words, a Lichen is not an individual, but a 

 tirm of two individuals very unlike each other. This habit 



FIG. 70. A common lichen (Pliyscia] growing on bark, showing the spreading thallue 

 and the numerous dark disks (apothecia) bearing the asci. OAI.DWET.L. 



of living together has been called symbiosis, and the indi- 

 viduals entering into this relation are called symbionts. 



FIG. 71. A common foliose lichen (Paiinelid) growing upon a board, and showing 

 apothecia. CALDWEI.I.. 



