232 



THE ASCO-LICHENS 



size, forms of Morchella occasionally reaching the height of a 

 foot and some species of Gyromitra weigh over a pound. 



86. The Asco-lichens. — A second line of departure from the 

 Pezizales includes a large group of plants known as the lichen. 

 The great majority of these forms show strong evidence of rela- 



■•^^ 



Fig. 141. Common forms of the Helvellales: A, the morel, Morchella, 

 surface view at left and in section at right. The asci and paraphyses form 

 a hymenium over the honeycomb surface. B, Leotia, a small gelatinous 

 form of a light, bluish-green color. C, Geoglossum, a black tongue-like form. 

 In B and C the hymenium is confined to the upper enlarged portion of the 

 fungus. Both are common in boggy ground. 



tionship with the cup fungi in their reproductive processes and 

 it should be added that the sex organs are more suggestive of 

 the red algae than in any other group. A few species belong to 

 the third class of fungi, the basidiomycetes, but these plants show 

 the same general features as the asco-lichens and therefore a 

 consideration of the entire group may be taken up at this point. 

 These remarkable plants are of almost universal distribution upon 

 tree trunks, rocks, old fences and buildings, and upon the bare 

 earth, where they form variously colored incrustations or leaf- 

 like branching bodies (Fig. 142). 



The lichen is one of the most extraordinary plants in the 

 vegetable kingdom, since it is a union of two separate plants, a 

 fungus and an alga. Naturally the relationship of the lichens 

 to other groups of plants has been a matter of dispute, some 



