SEAWEEDS. 



129 



distinction, and the whole family, including both the 

 denizens of the sea and of fresh water, are ranged in 

 three divisions : the first olive in colour, with seeds or 

 spores also olive, and a secondaiy form of fructification 

 called antheridia, containing orange bodies, which, when 

 seen under the microscope, exhibit lively motion as if of 

 animal life. The second division are red weeds. They 

 have fruit of two kinds, each one on different plants; 

 the one called spores is contained in cases dispersed 

 through the substances of the weed ; the other, called 

 tetraspores, is often external. The third division con- 

 tains, as a rule, green weeds, though there are some 

 exceptions in favour of purple. The sp>ores are often 

 endowed with motion, and the vesicles, or secondary form 

 of fruit, are external. Some of these green weeds belong 

 to the sea, but many inhabit freshwater. In size, Algae 

 vary from simple microscopic cells to branched woody 

 plants, many fathoms in length. The structure of them 

 all is very simple, consisting of roundish cells either 

 adhering firmly to each other, or connected by transparent 

 gelatine. 



The first heap we examined was in a great measure 

 composed of the blackish strap- 

 shaped fronds of the Sea-oak. 

 These were branched and thick- 

 ened at intervals of less than '•an 

 inch with bladder-like air vessels. 

 The whole plant looked like 

 strips of thick dark leather. This 

 is the first British member of the 

 Olive family, or Melanospennce. 



2 SARGASSUM. 1 HALIDRYS. 



