  Some of the more technical terms about which there might be some doubt, as they are not always accompanied by explanations in the text, are here briefly defined. Anatomy.—The study of the details and relative arrangements of the internal features of plants; in particular, the relations of the different tissue systems. Bracts.—Organs of the nature of leaves, though not usual foliage leaves. They often surround fructifications, and are generally brown and scaly, though they may be brightly coloured or merely green. Calcareous.—Containing earthy carbonates, particularly calcium carbonate (chalk). Cambium.—Narrow living cells, which are constantly dividing and giving rise to new tissues (see fig. 33, p. 57). Carbonates, as used in this book, refer to the combinations of some earthy mineral, such as calcium or magnesium, combined with carbonic acid gas and oxygen, formula CaCO3, MgCO3, &c. Carpel.—The closed structure covering the seeds which grow attached to it. The “husk” of a peapod is a carpel. Cell.—The unit of a plant body. Fundamentally a mass of living protoplasm with its nucleus, surrounded in most cases by a wall. Mature cells show many varieties of shape and organization. See Chapter VI, p. 54. Centrifugal.—Wood or other tissues developed away from the centre of the stem. See fig. 65, p. 97. Centripetal.—Wood or other tissues developed towards the centre of the stem. See fig. 65, p. 97. Chloroplast.—The microscopic coloured masses, usually round, green bodies, in the cells of plants which are actively assimilating. Coal Balls.—Masses of carbonate of calcium, magnesium, &c., generally of roundish form, which are found embedded in the coal, and contain petrified plant tissues. See p. 28. Concretions.—Roundish mineral masses, formed in concentric layers, like the coats of an onion. See p. 27. Cotyledons.—The first leaves of an embryo. In many cases packed with food and filling the seed. See fig. 58. Cross Fertilization.—The fusion of male and female cells from different plants. Cuticle.—A skin of a special chemical nature which forms on the outer wall of the epidermis cells. See p. 54, fig. 21. Earth Movements.—The gradual shifting of the level of the land, and the bending and contortions of rocks which result from the slow shrinking of the earth’s surface, and give rise to earthquakes and volcanic action. Embryo.—The very young plant, sometimes consisting of only a few delicate cells, which results from the divisions of the fertilized egg cell. The embryo is an essential part of modern seeds, and often fills the whole seed, as in a bean, where the two fleshy masses filling it are the two first leaves of the embryo. See fig. 58, p. 77. Endodermis.—The specialized layer of cells forming a sheath round the vascular tissue. See p. 55. Endosperm.—The many-celled tissue which fills the large “spore” in the Gymnosperm seed, into which the embryo finally grows. See fig. 57. Epidermis.—Outer layer of cells, which forms a skin, in the multicellular plants. See fig. 21, p. 54. Fruit.—Essentially consisting of a seed or seeds, enclosed in some surrounding tissues, which may be only those of the carpel, or may also be other parts of the flower fused to it. Thus a peapod is a fruit, containing the peas, which are seeds. Gannister.—A very hard, gritty rock found below some coal seams. See p. 25. Genus.—A small group within a family which includes all the plants very like each other, to which are all given the same “surname”; e.g. Pinus montana, Pinus sylvestris, Pinus Pinaster, &c. &c., are all members of the genus Pinus, and would be called “pine trees” in general (see “Species”). HyphÆ.—The delicate elongated cells of Fungi. Molecule.—The group of chemical elements, in a definite proportion, which is the basis of any compound substance; e.g. two atoms of hydrogen and one atom of oxygen form a molecule of water, H2O. A lime carbonate molecule (see definition of “Carbonate”) is represented as CaCO3. Monostelic.—A type of stem that contains only one stele. Morphology.—The study of the features of plants, their shapes and relations, and the theories regarding the origin of the organs. Nucellus.—The tissue in a Gymnosperm seed in which the large “spore” develops. See figs. 55 and 56, p. 76. Nucleus.—The more compact mass of protoplasm in the centre of each living cell, which controls its growth and division. See fig. 17, n. PalÆobotany.—The study of fossil plants. PalÆontology.—The study of fossil organisms, both plants and animals. Petiole.—The stalk of a leaf, which attaches it to the stem. Phloem.—Commonly called “bast”. The elongated vessel-like cells which conduct the manufactured food. See p. 57. Pollen Chamber.—The cavity inside a Gymnosperm seed in which the pollen grains rest for some time before giving out the male cells which fertilize the egg-cell in the seed. See p. 76. Polystelic.—A type of stem that appears, in any transverse section, to contain several steles. See note on the use of the word on p. 63. Protoplasm.—The colourless, constantly moving mass of finely granulated, jelly-like substance, which is the essentially living part of both plants and animals. Rock.—Used by a geologist for all kinds of earth layers. Clay, and even gravel, are “rocks” in a geological sense. Roof, of a coal seam. The layers of rock—usually shale, limestone, or sandstone—which lie just above the coal. See p. 24. Sclerenchyma.—Cells with very thick walls, specially modified for strengthening the tissues. See fig. 28, p. 56. Seed.—Essentially consisting of a young embryo and the tissues round it, which are enclosed in a double coat. See definition of “Fruit”. Shale.—A fine-grained soft rock, formed of dried and pressed mud or silt, which tends to split into thin sheets, on the surface of which fossils are often found. Species.—Individuals which in all essentials are identical are said to be of the same species. As there are many variations which are not essential, it is sometimes far from easy to draw the boundary between actual species. The specific name comes after that of the genus, e.g. Pinus montana is a species of the genus Pinus, as is also Pinus sylvestris. See “Genus”. Sporangium.—The saclike case which contains the spores. See figs. 52 and 53, p. 75. Spore.—A single cell (generally protected by a cell wall) which has the power of germinating and reproducing the plant of which it is the reproductive body. See p. 75. Sporophyll.—A leaf or part of a leaf which bears spores or seeds, and which may be much or little modified. Stele.—A strand of vascular tissue completely enclosed in an endodermis. See p. 62. Stigma.—A special protuberance of the carpel in flowering plants which catches the pollen grains. Stomates.—Breathing pores in the epidermis, which form as a space between two curved liplike cells. See fig. 23, p. 54. Tetrads.—Groups of four cells which develop by the division of a single cell called the “mother cell”. Spores and pollen grains are nearly always formed in this way. See p. 75. Tracheid.—A cell specially modified for conducting or storing of water, often much elongated. The long wood cells of Ferns and Gymnosperms are tracheids. Underclay.—The fine clay found immediately below some coal seams. See p. 24. Vascular Tissue.—The elongated cells which are specialized for conduction of water and semifluid foodstuffs. |
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