552 



THE PATHOGENIC ALGAE. 



Mycoidaceae. 



Cephaleuros Mycoidea, Karsten^ {Mycoidea parasitica. 

 Cunning.).^ This alga is epiphytic on the leaves of most trees 

 and shrubs in the tropics. It varies considerably in its appear- 



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Fig. 328. — Cephaleuros Mycoidea. Section through the epidermis of a leaf of CaTntllia, 

 showing the thallus-like disc with haustoria. (After Gxinningiiani.) 



ance, but generally forms flattened thalloid discs several layers 

 of cells thick and attached firmly to leaves by means of rhizoids 

 (Fig. 328). Hairs are produced from the thallus-dises, especially 



Fig. 329. — Cephaleuros Mycoidea. Section through part of an attacked leaf of 

 Camellia. The epidermal layer has been ruptured, and haustoria from the algal 

 disc penetrate to the tissues. The dark-shaded portion is that killed by the 

 alga. (After Cunningham.) 



the older ones ; in addition, sporangial structures are also developed 

 and give off biciliate swarm-spores. The discs form a kind of 

 cuticle which becomes completely fused with that of the leaves. 



' Karsten, AmmZ. dujardin. botan. de Buitenzorg, Vol. x., 1891. 



^ Cunningham, Trans, of Linnean Soc. of London, 1880 ; H. M. Ward {idem), 

 1884. 



