THE TI/ALLOPUYTA 



303 



pushed upward at the end of a stalk. Tlic rank odor a1 tracts 

 to those fungi many carrion-loving insects. 



Lichens. In addition to the algae and fungi, the thallophytcs 

 include a remarkable group of composite plants, the Uchem. 

 The.se are fungi in the mycelium of which groups of algal cells are 

 entangled (Fig. 181). The advantage to the fungus of this 

 intimate association is evident, and the 

 alga is also probably benefited to some 

 extent. Instead of regarding this as a 

 case of true symbiosis, however, most 

 botanists look upon the fungus as parasitic 

 on the algal member of the combination, 

 even though this parasitism is very mild. 

 The two component plants have been arti- 

 ficially separated, and it has been found 

 that the alga can exist independently in 

 every case but that the fungus is unable to 

 do so. Lichens have also been "synthe- 

 sized" experimentally by bringing appro- 

 priate algae and fungi together. The 

 fungus members of lichens are almost 

 always ascomycetes. A number of different 

 algae are represented in lichens but these 

 belong mainly to the Cyanophyceae and to 

 the Protococcales. All are very simple in 

 character. The fungus mycelium is often 

 somewhat gelatinous and thus tends to 

 absorb water readily and hold it tenaciously. 

 It is much more compact, differentiated, the stink-horn. Fructi- 



1 J.1 i.i,j.r J- fication, showing the 



and dennite in shape than that oi ordmary gieba, above at the end 

 fungi and is essentially a flat thallus (Fig. of the stalk, and the 



ioo\ rrii. • X r XI 11 remains of the pendium 



182). Ihree mam types of thallus are below, 

 recognized: The crustaceous, which grows 



closely appressed to the surface of rocks, bark and similar struc- 

 tures; the foliose, in which the thallus is broader and somewhat 

 branched, suggesting that of the liverworts; and the fruticose, in 

 which it is slender and vcM-y much brancluMJ and may eitluM' he 

 erect or hanging. 



Asexual multiplication is accomplisluHl by the production and 

 dispersal of soredid or small l)its of mycelium in which a few algal 

 C(>lls are entangle*!. The fructifications are conspicuous, and the 



Fig. lSO.~Phal(us, 



