FAMILY ECTOCARPACE.E I SPHACELAUIA. 345 



of the distinction between Root, Stem, and Leaf ; but tbis distinc- 

 tion is very imperfectly carried out, tbe root-like and stem-like por- 

 tions serving for little else than tbe mechanical attachment of the 

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

 ing its own nutriment, so that no transmission of fluid takes place 

 from one portion of the fabric to another. Hence we find that there 

 is not yet any departure from the simple Cellular type of structure; 

 the only modification 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 

 ox 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, notwithstanding, contains some of the most elegant and de- 

 licate structures that are anywhere 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 deUcate 

 Sea-weed, which is very commonly found parasitic upon larger 

 Algae, either near low-water-mark or altogether submerged ; its 

 general form being remarkably characterized by a symmetry that 

 extends also to the individual branches (Fig. 161, a), the ends of 

 which, however, have a decayed look that seems to have suggested 

 the name of the genus (from the Greek <rtpa.Ki\os gangrene). 

 From the recent observations of Pringsheim, it appears that 

 this apparent decay really consists in the resolution of the endo- 

 chrome of the terminal cells into Antherozoids, which, when ma- 

 ture, escape by an opening with a long tubular neck, which forms 

 itself in the wall of the sphacela. The same happens with the 

 terminal cells of the peculiar lateral branchlets, which are known 

 as propagative 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 considered as propagative buds in other 

 individuals. 



258. The study of the higher and larger members of this group 

 has recently come to present a new and very attractive source of 

 interest to the Microscopist, in consequence of the discovery of the 

 truly Sexual nature of their fructification ; and we shall take that 

 of a common species of Fucus as the type of that of the order gene- 

 rally. The ' Receptacles,' which are borne at the extremities of 

 the fronds, here contain both ' Sperm-cells ' and ' Grerm-cells ;' in 

 some other species, however, these are disposed in different Re- 

 ceptacles on the same plant ; whilst in the commonest of all 

 F. vesiculosus (bladder-wrack), they are limited to different indi- 

 viduals.* When a section is made through one of the flattened 



* It was at first stated by MM. Thuret and Decaisne that this species 

 was sometimes dioecious, sometimes hermaphrodite ; but they now con- 

 sider the hermaphrodite form to be a distinct species, the F. plati/carpus 

 described above. 



