438 



BOTANY OF THE LIVING PLANT 



The fruit-bodies are very complex in some of the larger saprophytic 

 Ascomycetes. An extreme case is seen in the edible Morel (Morchella 

 esculenta), in which the external hymenial surface is convoluted so 

 as to accommodate a vast number of asci. It is possible to refer this 

 to an elaboration of the Discomycetous type, as it is seen in Peziza 

 (Fig. 370). But in the Truffle (Tuber) the equally numerous asci are 

 borne internally, in the large underground tuberous fruit (Fig. 371). 



ASCO-LICHENES 



There is a series of Ascomycetous Fungi which live in symbiotic 

 relation with Algae, and thus constitute compound bodies which are 

 called Lichens. The physio- 

 logical relation of the two 

 distinct organisms is not unlike 

 that of the Fungus and Host- 

 plant in mycorhiza, but there is 

 here no intra-cellular digestion 



./ n 



FIG. 372. 



A=Xanthoria (Parmelta) parteiinq, the common foliaceous yellow Lichen. 

 B=Cladonia rangifera, a fruticose Lichen. Both bear ascus-fruits, and are shown 

 natural size. (After Strasburger.) 



(Chapter XL). 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 grey to more vivid yellow, or even red. They are curiously 



