210 



STRUCTUEAL BOTANY 



the carpogonium. So far, therefore, as the act of fertili- 

 sation is concerned, the Florideae do not differ from other 

 sexual organisms. 



The result of fertilisation, however, is not the formation 

 of a single ob'spore, but the development of a whole fruit. 

 The fertilised carpogonium is cut off from the trichogyne 



by a plug of cell-wall, and then 

 sends out short branches, which 

 come into close contact with the 

 auxiliary cells on either side ; 

 there is an actual union of the cell 

 contents of the carpogonium with 

 those of the two auxiliary cells, 

 but the nuclei do not fuse. Each 

 auxiliary cell now divides by a 

 transverse wall (see Fig. 91, c) ; 

 the upper of the two cells in each 

 case becomes a placenta which 

 corymbosum ; part of a gives rise to the spores. Calli- 

 show^^thT^Uest Mamnion is different from most of 

 stage of development of the simpler red seaweeds in so far 

 fertil^S^TheySe as it regularly forms two fruits 



by the growth and from each procarpium, whereas its 

 division of the two ... ,, , 



auxiliary cells. Magni- near allies usually torm one only. 



fied 250. (After Thuret Each placenta buds out into a 



number of cells, which themselves 



divide repeatedly, so that eventually two large groups 

 of cells arise, one on each side of the filament (see Fig. 

 88, c). The groups are really built up of a system of 

 very short and densely crowded unicellular branches, 

 those of each cluster all springing ultimately from the 

 placenta belonging to it. The whole fruit is enclosed in 

 a gelatinous cell - wall, but no cell - walls are formed 



