68 



CHLOROPHYCEAE 



Trentepohliaceae : Cephaleuros (cephal, head; euros ^ broad). 

 Fig. 48. 



These grow as epiphytes and parasites on and in the leaves of 

 various phanerogams. The plants are composed of one or more 

 branched interwoven threads from which vertical filaments arise 

 that bear clusters of stalked sporangia very like those of Trente- 

 pohlia. Some species bear sterile erect filaments that terminate in 



Fig. 48. Cephaleuros. A, leaf of Magnolia infected with C. virescens. B, trans- 

 verse section of leaf of Michelia fuscata showing filaments and rhizoids (r) of 

 C virescens. C, transverse section of leaf of Zizyphus with C minimus showing 

 sporangial branches. D, sporangia of C mycoidea. (A, after Smith; B, C, after 

 Fritsch; D, after Oltmanns.) 



hairs, whilst the parasitic species possess rhizoids which penetrate 

 the cells of the host, although it has not been clearly established 

 whether the host cells are killed before or after penetration. Cepha- 

 leuros virescens forms the red rust of the tea plant which may cause 

 much economic damage, but the attack is only serious when the 

 tea tree is growing slowly, because during periods of rapid growth 

 the alga is continually being shed by exfoliation of the outer tissues. 

 The disease cannot be controlled by spraying with poisons, but the 

 bushes can be made less susceptible to attack by treating the soil 

 with potash. The genus is confined to the tropics. 



