Hydrangea

Hydrangea, common name for certain deciduous and evergreen shrubs and woody vines. Hydrangeas are native to Asia and the Americas. The flowers are borne in clusters, the outermost flowers of which consist of a colored, membranous envelope, but the inner flowers of which have an eight- to ten-ribbed, tubular envelope, four or five ovate petals, eight to ten slender stamens, and a two-celled pistil. The fruit is a many-seeded capsule. The wild hydrangea of the eastern United States is an erect shrub that grows up to 3 m (up to 10 ft) high and bears white flowers in round clusters. The showier hydrangeas are cultivated Asian species, such as a typical cultivar of the hortensia, which grows up to 3.6 m (up to 12 ft) high; has broad, thick, shining leaves; and produces white, blue, or pink, flowers in round or flat clusters. The mock orange, a separate genus of the same family, also produces showy white flowers.

Scientific classification: The genus Hydrangea belongs to the family Saxifragaceae. The wild hydrangea is classified as Hydrangea arborescens and the typical cultivar of the hortensia as Hydrangea macrophylla cultivar hortensia.

Fennel

Fennel, common name for a perennial plant (see Parsley), characterized chiefly by its aromatic leaves and seeds. Fennel grows from about 61 to 122 cm (about 24 to 48 in) in height and has small yellow flowers. The common fennel is cultivated in both Europe and America. Its leaves and seeds are used for flavoring. Another variety, called variously Florence fennel, sweet fennel, Italian fennel, or Cretan fennel, is cultivated in southern Europe. The bases of the leafstalks of Florence fennel are greatly enlarged and form a bulbous structure, which is bleached by earthing and then eaten raw or cooked. The seed of Florence fennel is used widely in Italy as an aromatic condiment and as a medicine.

Scientific classification: Fennel belongs to the family Apiaceae (formerly Umbelliferae). It is classified as Foeniculum vulgare. The common fennel is classified as Foeniculum vulgare variety azoricum, and the Florence fennel as Foeniculum vulgare variety dulce.

Gametophytes

Spore, term applied to a specially modified asexual reproductive cell produced by many fungi and plants and by some protozoans. The spore is resistant to heat, drought, and other adverse conditions, remaining in a resting state until the environment is favorable for development or germination. Many bacteria (see Prokaryote) concentrate their cytoplasm and encapsulate under unfavorable conditions; these resting stages are generally called spores, but they are not reproductive cells and are therefore not comparable to the spores of other organisms.

Spores are usually produced by the division of cells within a structure called a sporangium. In bryophytes and most ferns, horsetails, club mosses, and whisk ferns, spores give rise to the same kind of plants as the parents, which are thus called homosporous. But in a few of those just mentioned and in all seed plants, some spores grow into sexual plants (gametophytes) that produce male gametes (sex cells), while others grow into sexual plants that produce female gametes; parent plants producing such spores are called heterosporous. Spores that give rise to male gametophytes are called microspores; spores giving rise to female gametophytes are known as megaspores. In seed plants, male gametophytes are known as pollen grains, and female gametophytes are called embryo sacs. Thick-walled resting zygotes (cells formed by the union of gametes) resemble spores and are called zygospores or oospores.

Brown Algae

Brown Algae, about 1500 species of almost exclusively marine, brown-colored algae, known as seaweeds, that make up the brown algae phylum in the protist kingdom. They are found mainly in the tidal zones of temperate to polar seas, but some exist in the deep ocean. Brown algae are the largest of the algae; well-known forms include the giant kelp and the free-floating sargassum weed. Their brown color is derived from the presence of the pigment fucoxanthin, which along with other xanthophyll pigments, masks the green color of the chlorophyll in the algal cells.

The brown algae are multicellular and have differentiated structures that, in some species, bear a superficial resemblance to the roots, stalks, and leaves of true plants. These structures, however, are quite different internally. The cell walls of the algae are made of a cellulose similar to that found in red algae; the outsides of the walls are covered by a gelatinous pectic compound called algin. The plants undergo an alternation of generations; the diploid phase (two sets of genes in a cell) is microscopic and brief, and the haploid phase (one set of genes in a cell) is macroscopic and comparatively long-lived. Brown algae such as kelp are harvested for use as an emulsion stabilizer, an ingredient of ice cream; as a fertilizer; as a vitamin-containing food source; and for iodine.

Scientific classification: Brown algae make up the phylum Phaeophyta in the kingdom Protista. Kelp are classified in the order Laminariales. Sargassum weed is classified in the genus Sargassum.

Desmid

Desmid, common name for numerous single-celled freshwater green algae. The cell is divided into two symmetrical halves, held together by an isthmus containing the nucleus. Each half of the cell contains a single chloroplast. Desmids sometimes grow in colonies, where individuals remain attached after cell division. Many species are capable of self-locomotion by gliding. They are phototropic; the direction of their movement is determined by their response to light.

Desmids reproduce both sexually and asexually. Asexually, the desmids reproduce by a simple division across the isthmus; the one cell becomes two. In sexual reproduction, the desmids come together in pairs and their cell contents fuse. From this fused body come two new desmids. Although this form of sexual reproduction does not increase the population, it does maintain genetic variation within the population.

Desmids of one common genus are crescent shaped and have a small vacuole at each end of the cell. These vacuoles contain minute crystals of gypsum, which are in constant Brownian motion.

Scientific classification: Desmids make up the family Desmidiaceae. Crescent-shaped desmids with vacuoles containing gypsum crystals make up the genus Closterium.