244 SEAWEEDS 



seas, the Corallines have a much wider range than the 

 animal corals, and occur in considerable numbers in 

 the colder regions of the ocean. On British shores, 

 Corallina, Jania, Lithothamnion, LithopJiyllum, Melo- 

 besia, and a very minute form, Schmitziella (incrusting 

 Cladophora pellucida), represent the family with a fair 

 number of species. 



The stony incrustation extends to all parts except 

 the reproductive organs. Tetraspores, antheridia, and 

 carpospores, are all formed in special conceptacular 

 bodies (Figs. 84 and 85). In the flat encrusting 

 forms these conceptacles appear as minute, wart-like 

 outgrowths from the sterile part of the thallus ; in 

 Corallina they occupy the summits of the branches ; 

 and in Amphiroa they are lateral. In Lithothamnion 

 these conceptacles are eventually overgrown by the 

 increasing growth in thickness of the thallus, and in 

 breaking down the stony substance they may be met 

 with as small cavities representing the conceptacles 

 of earlier periods of growth. 



The carpogonial branches occur, together with 

 numerous auxiliary cells, in special fertile portions of 

 the cortex. The auxiliary cells are joint cells of 

 peculiarly differentiated thallus filaments. On the 

 fertilisation of the carpogonium all, or nearly all, the 

 auxiliary cells near it become fused with it by means 

 of the ooblastema filament, forming a large ''conjuga- 

 tion cell." From its periphery minute gonimoblasts 

 arise, bearing chains of carpospores. The cystocarp 

 is here, therefore, a kind of syncarp, since it results 

 from the combination of numerous auxiliary cells 

 and their products into one common definite fruit, 



