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new function ; their cell-walls are quite thick, and contain a high 

 percentage of lichen-acids, which prevent their being eaten by- 

 visiting insects or snails. Like the rhizoids, the cilia are highly hy- 

 groscopic, and absorb moisture with great avidity ;' this can readily 

 be observed by bringing a drop of some colored liquid in contact 

 with their tips. It seems evident that the prime function of 

 the cilia is to retain and absorb drops of water; a second and 

 less important function is that of preventing crawling animals from 

 passing to the upper surface of the thallus (Zukal). 



I III. REPRODUCTIVE AND PROPAGATIVE ORGANS. 



I. THE APOTHECIA. 



The apothecia are the spore-bearing organs of lichens developed 

 from the fungal symbiont, although the algae enter into their formation 

 in the higher lichens (thalloid exciple) ; structurally, and in their 

 mode of development, they are closely related to the apothecia of the 

 Ascomycetes; their great variability in form and size will be more 

 fully discussed in the descriptions of families and genera. The great 

 majority of apothecia occur on the upper surface of the thallus, 

 either sessile or immersed ; in Nephroma, however, they occur on 

 the lower surface. Special morphological adaptations occcurring in 

 the apothecia, either for mechanical or protective purposes, will be 

 more fully discussed in another chapter. As in the treatment of the 

 thallus, we shall limit ourselves to the discussion of the general mor- 

 phology and physiology of the typically developed apothecium, 

 as it occurs in Sticta, Parmelia and other higher foliose lichens. 



(a) The Efithechmi. 



The old definition of epithecium is morphologically indefinite ; 

 as defined by Leighton and Nylander it is the colored disk of the 

 apothecium ; this colored disk, however, includes the upper parts of 

 the paraphyses as well as the remnants of the thallus which were 

 above the disk as the apothecium pushed its way through the upper 

 cortical layer ; it is, therefore, evident that the term epithecium in- 

 cludes two morphologically distinct tissues. I have decided to 

 designate only the remnant of the thallus as the epithecium proper ; 

 in the majority of mature apothecia this is scarcely recognizable ; it 

 consists of the broken down and gelatinized granular remnants of the 



