310 



Ulotrichales 



Cephalevros virescens Kunze ( = Mycoidea parasitica Cunningham) is a parasite on the 

 leaves of Camellia, Mangifera, Rhododendron, Thea, Croton, and various Ferns. In 

 North-east India and Assam it causes the ' Red Rust of Tea,' the most serious disease 

 to which the tea- plant (Thea sinensis) is liable in that part of the world, and it is as a 

 stem-parasite that it is so destructive (Mann & Hutchinson, '04 ; '07). The parasite 

 occurs on both leaves and young shoots (fig. 203 D and E), the latter being mostly 

 infected by zoogonidia from the fructifications of the algal thalli on the leaves. The 

 young shoots are particularly susceptible to attack owing to the rough character of the 



fPt 



m 



ts 



^z-m^m^ 



Fig. 203. A C, Phycopeltis epipliyton Millard. A, medium-sized thallns, with the cells in 

 outline only ; the five represented with double lines are empty zoogonidangia ; B, small 

 portion of thallus to show division of peripheral cells ; C, zoogonidium. D F, Cephaleuros 

 virescens Kunze. D, part of leaf of tea-plant with an epiphytic lichen (I) and the parasitic 

 Alga (a) ; E, tea-shoot attacked by Alga (a) F, part of transverse section of tea-leaf showing 

 the penetration of the Alga into the leaf; the algal cells are shaded. A, x 300 ; B and C, 

 x 900 (after Millard from Wille) ; D and E, natural size ; F, x about 60 (after Mann & 

 Hutchinson). 



bark, in the crevices of which the zoogonidia come to rest and germinate. The parasite 

 is only disastrous in its effect when, owing to want of vitality in the plant attacked, the 

 growth of the Alga is more rapid than the growth of the shoot, in which case the algal 

 filaments penetrate and destroy the tissues of the host. If the shoot is growing faster 

 than the Alga, the latter is removed by exfoliation of the outer tissues and no permanent 

 infection takes place (Mann & Hutchinson, '07). 



Some species of the Trentepohliacese have become constituents of the thalli of certain 

 Lichens (vide p. 141). 



