THE ALGJE 211 



between the individual cells, each of which, when all 

 the divisions are complete, becomes a spore, called for 

 distinction a carpospore, as it forms part of the sexually 

 produced fruit, or cystocarp. When ripe, the membrane 

 of the fruit bursts and the spores are set free. They 

 are large, uninucleate, deeply pigmented cells, destitute at 

 the time of their escape of any cell-wall. 



The main points in the development are : (1) fertilisa- 

 tion by means of a special receptive organ, or trichogyne ; 

 (2) union of the protoplasm of the fertilised cell with 

 that of neighbouring cells; (3) the production, as the 

 result of this union, of a complex fruit, including a great 

 number of spores. 



Callithamnion occupies a middle position among the 

 Florideae as regards the complexity of its spore-forma- 

 tion. The trichogyne is common to all Florideae, but 

 some few members of the order (e.g. Nemalion and 

 the fresh - water genus Batrachospermum) are simpler, 

 in that the carpogonium directly gives rise to the 

 spores, without any preliminary cell - fusion. Many 

 red seaweeds, however, are more complicated, repeated 

 cell-fusion taking place, with the result, in some cases, 

 that a number of fruits may be formed in consequence 

 of a single act of fertilisation; these fruits often arise 

 at a considerable distance from the directly fertilised 

 cell. 



In some respects the process of sexual reproduction 

 in the Florideae is more complex than in any other 

 plants. It offers the advantage that a single spermatium, 

 if it once reaches a trichogyne, may ensure the production 

 of a very large number of spores. In many cases a 

 further complication is due to the fact that a multicellular 

 envelope grows up around the spores. To the frequent 



