_Preservation._--The mosses may be dried under pressure, and preserved entire in the same manner as the ferns or the flowering plants. If simply dried without pressure, their structure can be readily made out at any future time, by immersing them in water, or by keeping them for a few hours in a moist atmosphere. The minute structures of mosses may be mounted in solution of chloride of calcium, or in glycerine; they keep extremely well without closing the cells. CHAPTER VII. ALGÆ (ALGA, SEA-WEED). The plants belonging to the Class Algæ grow in water, either in that of the sea or in fresh water; a few of them, however, being found on damp earth, damp walls, &c. The marine Algæ are commonly known as sea-weeds; but the fresh-water Algæ generally receive but little popular notice, forming, as they do, slimy masses or strata, of a green or brownish, sometimes red, colour. Algæ are of simple structure, consisting entirely of cells; in some these are single, in others, united end to end, to form threads or filaments, or grouped into a leaf-like expansion, or collected few together into a little spherical group or a flat plate. They possess none of the fibres, vessels, or ducts of the higher plants, although some long and slender cells, existing in the stalks of the fronds of the larger kinds, bear considerable resemblance to woody fibre. They exhibit no distinction of stem and leaf, but consist of fronds representing the stem and leaf combined and undistinguishable. And the term frond must be understood to signify the separate parts arising from the point of attachment when they are fixed; and in the case of those which are unattached or free, the entire plant is called a frond. The Algæ are divided into three Orders, viz. the Fucoid´eæ or olive-coloured Algæ, the Florid´eæ or red, and the Confervoid´eæ or green Algæ. FUCOID´EÆ, Fucoid Algæ, or Melanospor´eæ (μἑλας, black or dark). The plants composing this order form our largest sea-weeds, and are found everywhere in the sea and on the sea-shore. They are of an olive-green or olive-brown colour, and usually become darker on drying. PLATE IV. [PAGE 64.] MARINE ALGÆ. Fig. 1. _Dasya coccinea_, piece of. 2. _Dasya coccinea_, portion with capsule (ceramidium). 3. _Dasya coccinea_, portion of main filament. 4. _Dasya coccinea_, section of filament. 5. _Melobesia polymorpha._ 6. _Melobesia polymorpha_, portion with capsules (ceramidia). 7. _Jania rubens._ 8. _Jania rubens._ 9. _Lithocystis Allmanni._ 10. _Ceramium nodosum._ 11. _Ceramium nodosum_, filament. 12. _Ceramium rubrum_, filament. 13. _Ceramium rubrum_, tetraspore. 14. _Ceramium rubrum_, end of filament. 15. _Ceramium rubrum_, capsule (favella). 16. _Fucus vesiculosus_, receptacles of. 17. _Fucus vesiculosus_, capsules (conceptacles). 18. _Fucus serratus_, antheridial conceptacles. 19. Spore of _Fucus vesiculosus_. 20. Antheridia of _Fucus serratus_. 21. _Plocamium coccineum_, sporophyll.