Fig. 12l.Me.<ioyloi(i 

 vermicularis. 



ALG.E. 211 



Stems and leaves ; and even in these, what appears a stem 



in the old plant has already served, 



at an earlier period of growth, either 



as a leaf, as in Sargassum and 



Systoseira, or as the mid-rib of a 



leaf, as in Delesseria. 



" The substance of which the 

 frond consists is as variable as the 

 form. Some are mere masses of 

 slime or jelly, so loose that they fall 

 to pieces on being removed from 

 the water; others resemble, in feel 

 and appearance, threads of silk; 

 some are stiff and horny; others 

 are cartilaginous, or with aspect 

 and elasticity of gristle ; others 

 tough and coriaceous, resembling 

 leather ; while the stems of some 

 of the larger kinds are almost woody. The leaves of 

 some are delicately membrauaceous, glossy, transparent; 

 of others, coarse and thick, and either wholly destitute of 

 nerves, or furnished with more or less defined ribs ; or 

 beautifully veined. 



" In structure, whilst there is a great variety among 

 the different tribes of algae, we find, in material points, 

 a perfect similarity among all. All consist of simple cel- 

 lular tissue, or of its elements, gelatine, membrane, and 

 endochrome, variously elaborated and perfected. No vessels 

 or ducts have been discovered in any, nor does woody fibre 

 exist among them. 



" The cellular tissue of algce presents some varieties. 

 The most common form of the cellule is cylindrical, often 

 of very small diameter, in proportion to its length ; and in 

 such cases the cellules always cohere by the ends into 

 threads or filaments, bundles of which, either branched or 

 single, form the fronds by lateral cohesion. 



" In colour, the algce exhibit three principal varieties, 

 with, of course, numerous intermediate shades, namely, 

 Grass-green, Olivaceous, and Red. The grass-green is cha- 

 racteristic of those found in fresh water, or in very shallow 

 parts of the sea, along the shores, and generally above 

 p 2 



