ASCOMYCETES 



427 



asci are borne internally, in the large underground tuberous fruit 



(Fig. 325). 



ASCOLICHENES. 



There is a series of Ascomycetous Fungi which live in symbiotic 

 relation with Algae, and thus constitute compound bodies which are 

 called Lichens. The physiological relation of the two distinct organ- 

 isms is not unlike that of the Fungus and Host-plant in mycorrhiza, 



Fig. 324. 



Morchella esculenta, the fruiting 

 body of the Morel. The convo- 

 luted folds of surface are covered 

 by the hymenial layer, bearing 

 asci. (* nat. size.) (After Stras- 

 burger. 



Fig. 325. 



a Truffle. The fructification in vertical 

 a = cortex. c=dark veins of compact 

 hvphae. d = air-containing tissue, h = ascogenous hyphae, 

 with numerous asci. (After Tulasne ; from Strasburger.) 



Tuber rufutn 

 section ( x 5). 



but there is here no intra-cellular digestion (Chapter XII.). The 

 Lichens are very various in form. In simple cases they may be 

 filamentous, as in Ephebe, which is like a filamentous Alga with a 

 fungus growing in its mucilaginous walls. Some appear as flat 

 gelatinous thalli, readily swelling with water, as in Collema, which is 

 based upon the gelatinous Alga, Nostoc. Others are more firm in 

 texture, and form variously flattened thalli, more or less closely 

 attached to the substratum of rocks, roofs, or tree-trunks, etc. Others 

 again are erect or pendulous, and often branched, rising freely from 

 their base of attachment. In texture they are brittle when dry, but 

 more or less leathery when moist, and they vary greatly in colour 

 from g«rey to more vivid yellow, or even red. They are curiously 



