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 CaCO_3, MgCO_3, &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.