SECT. ii. FRUCTIFICATION OF FUCUS. 253 



a midrib with air-vessels, generally in pairs on each 

 side of it, formed by the inflation of the frond ; these 

 vessels, however, are frequently wanting, for it is the 

 most variable in form and most widely spread of the 

 Fuci. The fructification of this group is contained in 

 large clavate receptacles or expansions of an orange or 

 greenish yellow colour situated at the extremities of 

 borders of the branches. 



MM. Thuret and Decaisne discovered, by microscopic 

 investigation, that the fuci have a truly sexual fructifi- 

 cation, consisting of male and female cells inclosed in 

 these receptacles. In the common Fucus vesiculosus it 

 was found that the male and female cells are either in 

 different individuals, or in different conceptacles on the 

 same individual ; whilst in the Fucus platy carpus, both 

 the male and female cells were found to be contained 

 in a globular cavity enclosed in the flattened receptacles 

 which grow at the extremities of the branches. The 

 cavity is lined with jointed hair-like filaments formed 

 of cells, some of which are so long as to project through 

 a pore on the surface of the receptacle in a spreading 

 brush (see fig. 31, where the whole is highly magnified). 

 Towards maturity, the cells of some of these filaments 

 assume an ovoid form ; the white viscous, granular 

 matter in their interior acquires an orange hue, and is 

 divided into a multitude of hyaline particles, each having 

 an orange spot and two cilia of unequal lengths, which 

 enable these spermatozoids to swim with great vivacity 

 in the water as soon as they are set free by the rupture 

 of the cell in which they are inclosed. Besides these, 

 dark olive-green female cells, of a large pyriform shape, 

 are fixed to the walls of the same cavity by very short 

 stems; their contents spontaneously divide into eight 

 spore cells, never more ; each contains a colourless 

 viscous liquid, which is mixed with protein and yellow- 

 green matter, and is inclosed in a double coat. 'The 



