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. FOOTNOTES [1]My book was entirely written before the second edition of Scott’s _Studies_ appeared, which, had it been available, would have tempted me to escape some of the labour several of the chapters of this little book involved. [2]The student would do well to read up the general geology of this very interesting subject. Such books as Lyell’s _Principles of Geology_, Geikie’s textbooks, and many others, provide information about the process of “mountain building” on which the form of our coalfields depends. A good elementary account is to be found in Watt’s _Geology for Beginners_, p. 96 _et seq._ [3]See note on p. 28. [4]This refers only to the “coal-ball”-bearing seams; there are many other coals which have certainly collected in other ways. See Stopes & Watson, Appendix, p. 187. [5]For a detailed list of the strata refer to Watts, p. 219 (see Appendix). [6]Though the Angiosperm was not then evolved, the Gymnosperm stem has distinct vascular bundles arranged as are those of the Angiosperm, the difference here lies in the type of wood cells.