F UNO I. LICHEXS. 



125 



8. Palmellaceae Many fruticose and foliaceous Lichens. 



Cystococcus humicola . . Physcia, Cladonia, Evernia, Usncn, l'<n'<>p%on, 



Anaptychia. 

 Pleurococats Endocarpon and various crustaceous Lichens. 



9. Coleochaeteae (Phyllactidiuntf- .Opegrapha filicina. 



The influence of the hyphae of the Fungus on the gonidia has been already alluded 

 to in the description of the hymenial gonidia. This influence is different in different 

 species. It is often scarcely perceptible, especially if the gonidia are unicellular 

 Algae, but very striking sometimes and especially in the case of filamentous Algae, 

 using that term in the widest sense. The filaments become crooked, divide into short 

 pieces, or separate into single cells, as in Opegrapha varia, the gonidia of which 

 belong to the filamentous Alga Chroolepus. At the margin of the thallus there are 



FIG. 84. Examples of various Algae which are employed as the gonidia of Lichens. /: indicates always the 

 hypha of the Fungus, g the gonidium. A germinating spore J of Physcia pariefinti, the ^rnn-tubc of which adl 

 closely to Protococcns viridis. B a filament of Scytonema with hyphae of Stcreocaiilon rauiit/osits twined round it. 

 C from the thallus of the Lichen PJiysma chalaganiiin ; a liyphal branch is entering a cell of the nostoc filnnirtit 

 (gonidium). D from the thallus of the Lichen Syiialissa symplwrca ; the gonidia are the Alga Glococafsa. 1 : . from 

 the thallus of the Lichen Cladonia fttrcata ; the gonidia which are being surrounded by the hyphae are the cells of Pro- 

 tococcus. After Bornet. A, C, D, E magn. 950, B 650 times. 



perfect filaments of Chroolepus still to be seen ; but as they become surrounded by the 

 hyphae they break up into short pieces or into single cells. On the other hand, we find 

 in old specimens of Op. varia that the gonidia have reassumed their normal appearance; 

 they elongate, form straight filaments, and produce the zoosporangia of the algal genus 

 Chroolepus. The gelatinous investment possessed by many Algae which serve as 

 Lichen-gonidia disappears in the Lichen-thallus. Among the most remarkable arc 

 the cases where the branches of the hyphae penetrate into the gonidia, as in Anio/tiia 

 and Physma (Fig. 84) ; this gave occasion to the old and erroneous notion that gonidia 



1 The systematic position of this Alga is still uncertain owing to our ignorance of its organs of 

 reproduction; the vegetative state however resembles Colcochaelc, and like it Intins l.mad di4. 

 on leaves and other objects. 



