LICHENS OF THE STATE OF WASHINGTON 



By 

 Grace E. Howard 



INTRODUCTION 



Lichens belong to the Thallophytes, the lowest of the great divisions of 

 the plant kingdom. A lichen consists of a fungus and an alga living together 

 in a large degree of mutual benefit. The alga contains chlorophyll, which 

 enables it to carry on photosynthesis and make carbohydrates for the part- 

 nership (consortium) ; the fungus absorbs both water and mineral nutrients 

 and also synthesizes the proteins. Furthermore, the fungus determines the 

 form, shape, size, and strength of the organism. In a few lichens the alga 

 has been isolated and grown in pure culture ; this has also been done with 

 the fungus. However, it is doubtful if they ever become separated in nature. 

 These algal lichens can be referred to present-day genera and often even to 

 species ; but the fungi cannot be placed, with any degree of certainty, in any 

 of our present-day genera. Hence, the identity of the fungus seems to have 

 been changed much more than that of the alga. In only three genera is the 

 fungus a Basidiomycete ; in all other genera it is an Ascomycete. The alga 

 belongs either to the Cyanophyceae or to the Chlorophyceae. 



It was believed by earlier students that the relationship between the alga 

 and the fungus was parasitism ; this view is still held by some students today. 

 When a lichen spore germinates it produces only the fungal hyphae and 

 not a lichen. Because of this fact it has been said that there are no true 

 species of lichens. Before a lichen can develop, these fungal hyphae must 

 grow around some algal cells, entangling them and penetrating their cell 

 walls with haustoria, so that the fungus may be supplied with the neces- 

 sary carbohydrates ; furthermore, in some lichens the algae grow completely 

 inside the fungal hyphae. It is true that dead algae have been reported 

 within the lichen thallus, a point in favor of parasitism. 



Other students consider this relationship to be a symbiosis. Even though 

 the carbohydrates for a lichen are made by the algae, they receive in return 

 an increased amount of light ; they also receive water and proteins from the 

 fungi. The algae are benefited greatly by the larger variety of habitats in 

 which they are able to grow while living in this symbiotic state, since lichens 

 have a wider distribution than any other group of plants. For these reasons, 

 I consider this relationship a symbiosis. The continued healthy and sturdy 

 growth of lichens, under adverse conditions, adds strength to this idea. 



Based upon habit of growth, lichens are classified as crustose, foliose, and 



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