332 



THE MICROSCOPE AND ITS REVELATIONS. 



exactly the same structure, and performs the same actions, as every 

 other part; living for and ly itself alone. And though, when we 

 pass to the higher Sea-weeds, such as the common Fucus and Laminaria, 

 we observe a certain foreshadowing of the distinction between Root, 

 Stem, and Leaf, this distinction is very imperfectly carried out; the root- 

 like and stem-like portions serving for little else than the mechanical at- 

 tachment of the leaf -like part of the plant,- and each still absorbing and 

 assimilating its own nutriment, so that no transmission of fluid takes 

 place from one portion of the fabric to another. There is not yet any 



departure from the simply cellular 

 type of structure; the only modi- 

 fication being that the several 

 layers of cells, where many exist, 

 are of different sizes and shapes, 

 the texture being usually closer 

 on the exterior and looser within; 

 and that the texture of the stem 

 and roots is denser than that of 

 the leaf-like expansions or fronds. 

 The group of Melanospermous or 

 olive-green sea-weeds, which in 

 the family Fucacece exhibits the 

 highest type of Algal structure, 

 presents us with the lowest in the 

 family Ectocarpacece ; which, not- 

 withstanding, contains some of the 

 most elegant fabrics that are any- 

 where to be found in the group, 

 the full beauty of which can only 

 be discerned by the Microscope. 

 Such is the case, for example, 

 with the Sphacelaria, a small and 

 delicate sea-weed, which is very 

 commonly found parasitic upon 

 larger Algae, either near low- water 

 mark, or altogether submerged; 

 its general form being remarkably 

 vertical section of receptacle of FUCUS piatycar- characterized by a symmetry that 



us, lined with filaments, among which, lie the extends also to the individual 



^^ l ^'^^^so^ C ont^in S octo- branches (Fig. 210, A), the ends 



of which, however, have a decayed 



look that seems to have suggested the name of the genus (from the 

 Greek Gcpaneho}, gangrene). This apparent decay really consists in the 

 resolution of the endochrome of the terminal cells in antherozoids, which 

 when mature, escape by an opening with a long tubular neck, which 

 forms itself in the wall of the sphacela. The same happens with the ter- 

 minal cells of the peculiar lateral branchlets, which are known as propa- 

 gative buds, as is shown at B. The germ-cells have not been certainly 

 recognized; but they are believed to be produced in what have been con- 

 sidered as propagative buds in other individuals. 



328. In the Fucacece, the Generative apparatus is contained in the 

 bulbose ' receptacles/ which are borne at the extremities of the fronds. 

 In some species, as the Fucus platycarpus, the same receptacles contain 

 both ' sperm-cells ' and ( germ-cells;' in others, these two sexual ele- 

 ments are disposed in different receptacles on the same plant; whilst in the 



pus, 



