202 STRUCTUKAL BOTANY 



The shade of colour, produced by the combination of the 

 two pigments, varies much in different species, and in 

 different conditions of the same plant. Sometimes a 

 bright rose colour is the result, sometimes a rich purple, 

 sometimes a reddish brown, while in a few cases so 

 little red colouring matter is developed that the green 

 pigment becomes externally visible. 



All the plants which have any good claim to rank 

 as Florideae agree cloeely in their minute organisation, 

 methods of reproduction, and life-history; so that the whole 

 group is a manifestly natural one, though in the degree 

 of complexity of the thallus, and in the elaboration of 

 the reproductive processes, there is a great range of 

 variation. The Floridese stand almost completely 

 isolated in the vegetable kingdom as at present known 

 to us. They form a perfectly well-characterised group, 

 which attains a remarkably high development on its own 

 lines, especially as regards the process of sexual re- 

 production. We shall only be able to describe one 

 representative, and that one of the simpler members of 

 the division. 



TYPE XVI. CALLITHAMNION CORYMBOSUM 

 1. STRUCTURE 



The form of the thallus among red Algae is subject to 

 very great variations ; in some the thallus is finely, in 

 others more coarsely filamentous ; in some, again, it is 

 of stouter build and cylindrical form, while in others 

 the whole plant assumes a flattened leaf-like shape, or 

 consists of a short axis, bearing leaf-like appendages. 



The type which we have chosen is one of the simplest, 



