LICHEN ALGAE 



55 



RIVULARIA Thuret. In tufts fixed at the base and forming roundish 

 gelatinous colonies; colour, blue-green. The gonidium of Lichinaceae has 

 been identified as R. nitida Ag. 



Algae belonging to one or other of these genera of Myxophyceae also 

 combine with the hyphae of Archilichens to form cephalodia 1 and Krem- 

 pelhuber 2 has recorded and figured a blue-green alga, probably Gloeocapsa, 

 in Baeomyces paeminosus from the South Sea Islands. They also form the 

 gonidia in a few species and genera of such families as Stictaceae and 

 Peltigeraceae. 



b. CHLOROPHYCEAE ASSOCIATED WITH ARCHILICHENS. The lichens of 

 this group are by far the most numerous both in genera and species, though 

 fewer algal families are represented. 



Fam. PROTOCOCCACEAE. Consisting of globular single cells, aggregated 

 in loose colonies, dividing variously. 



i. PROTOCOCCUS VIRIDIS Ag. (Pleurococcus vulgaris Menegh., Cystococ- 

 cushumicola Naeg.). Cells dividing 

 into 2, 4 or 8 daughter-cells and 

 not separating readily; in exces- 

 sive moisture forming short fila- 

 ments. The cells contain parietal 

 chloroplasts, and, according to 

 Chodat 3 , are without a pyrenoid 

 (Fig. 22). This alga, and allied 

 species, forms the familiar green 

 coating of tree-trunks, walls etc., 

 and, in "lichenological literature, 

 are quoted as the gonidia of most 

 of the crustaceous foliose and fru- 

 ticose lichens. Chodat 3 , who has 

 recently made comparative artificial cultures of algae, throws doubt on the 

 identity of many such gonidia. He lays great emphasis on the presence or 

 absence of a pyrenoid in algal cells. West, on the contrary, considers the 

 pyrenoid as an inconstant character. Chodat insists that the gonidia that 

 contain pyrenoids belong to another genus, Cystococcus Chod. (non Naeg.), 

 a pyrenoid-containirig alga, which, in addition to multiplying by division 

 of the cells, also forms spores and zoospores when cultivated. He further 

 records the results of his cultures of gonidia, and finds that those taken 

 from closely related lichens, such as different species of Cladonia, though 

 they are alike morphologically, yet show constant variations in the culture 

 colonies. These, he holds, are sufficient to indicate difference of race if not 



Fig. 22. Plettrococcus vulgaris Menegh. (Protococ- 

 cus viridis Ag. ). chl. chloroplast ; /. protodertna 

 stage; pa, palmelloid stage; /_:', pyrenoid. x 520 

 (after West). 



1 See p. 133. 



Krempelhuber 1873. 



3 Chodat 1913. 



