LICHENS 



361 



part of which is used by 



the fungus. The Latter, 



after it has become ac- 

 customed to the alga, 



cannot live apart from 



it, and the alga, while 



it can live by itself, 



appears plump and pros- 

 perous when it is found 



surrounded by fungal 



threads. The partner- 

 ship, therefore, seems to 



be helpful to both plants. 



Such a relation between 



organisms is known as 



symbiosis (sim-bi-6'sis: 



life together ; Greek, 



syn, with ; bios, life). 



(Figures 386 and 387.) 



Lichens are interesting chiefly as representing this 



peculiar interdependence of plants. They have lit tit- or 



no economic importance, although in the 

 Arctic Regions they furnish a supply 

 of food for the reindeer. 



We close the study of the simplest 

 plants with the fungi. As in the ca 

 of the bacteria, men have Bpenl their 

 lives studying the fungi, especially 

 those which cause disease. Much lias 

 been accomplished, but a great deal 

 remains to be done in finding out the 

 cure for certain fungus diseases, espe- 

 cially those that attack vegetables which 



tion of Lichen. W6 use for food. 



Figure 386. — Lichens. 



