78 A LICHEN. 



ANNOTATIONS. 



The group of plants known as Lichens illustrates a 

 close symbiotic relationship between chlorophyll-bearing 

 and non-chlorophyll-bearing plants. The combination 

 known as one Lichen is really two plants living to- 

 gether. The fact that each is a distinct plant has been 

 proven by growing the individuals out of the Lichen 

 combination, and by growing Lichens by bringing to- 

 gether appropriate Algae and Fungi that did not previ- 

 ously live in such an association. 



The Fungus constructs an outside coating that seems 

 to protect the internal hyphae and the Algae. The Algae 

 are so placed as to be well exposed to light, enabling 

 them to manufacture food used by themselves and the 

 Fungi. Doubtless the Fungi assist also in the combina- 

 tion by absorbing materials, and attaching the Lichen 

 to its support. 



Difference of opinion exists as to whether the Fungus 

 is a parasite upon the Algae, or whether both Alga and 

 Fungi are benefited by this habit of living. It is known 

 that Lichens can live in many positions and climates 

 where neither Fungus nor Alga could live alone. 



In reproduction each plant is independent, there being 

 no Lichen spore in the sense that a single such spore will 

 produce a new Lichen. It is true that the Fungus uses 

 the Alga to nourish it in its process of reproduction, but 

 the spore formed does not reproduce the Alga. 



The forms and habits assumed by Lichens are quite 

 varied. Some are almost invisible scales adhering 

 closely to bark of trees and walls of rocks. Many others 



