THE FUNGI 97 



THE LICHENS 



In connection with the true Fungi there must be con- 

 sidered the Lichens. While there is no doubt that these 

 are sufficiently distinct to form a separate class, never- 

 theless their obvious relationship to other fungi, mostly 

 Ascomycetes, forbids the establishment of a subkingdom 

 coordinate with Algas and Fungi. 



These curious organisms exhibit a remarkable type 

 of parasitism, or perhaps better, s}^mbiosis, where two 

 plants, an alga and a fungus, are so intimately associ- 

 ated as practically to form a single plant. An exami- 

 nation of the thallus of a lichen shows it to be made 

 up of densely woven and more or less coherent hyphae, 

 among which are found numerous green cells. The 

 latter are usually aggregated near the outside of the 

 thallus, and a careful examination shows them to be 

 certain low algae, which can be readily identified as 

 species often growing quite apart from the lichen. 

 If these algae are isolated, and given proper conditions 

 for growth, they flourish perfectly, showing that they 

 are not, in any true sense of the word, really dependent 

 upon the lichen for their existence. While in some 

 respects the hyphre of most lichens differ somewhat 

 from those of other fungi, still the general structure is 

 very similar, and the fructification corresponds exactly 

 with that of typical fungi, especially the Ascomycetes, 

 to which most lichens are undoubtedly related. A few, 

 however, are Basidiomycetes. 



It was supposed by the earlier students of the lichens 

 that the green cells were direct outgrowths of the color- 

 less hyphas, but the more careful investigations of later 



H 



