571. The simple microscope may be reduced to a good lens or doublet, of an inch focus, mounted over a glass stage, so that it can be moved up and down and also sidewise, and with (or without) a little mirror underneath. A better one would have one or two additional lenses (say of half and of a quarter inch focus), a pretty large stage, on the glass of which several small objects can be placed and conveniently brought under the lens; and its height or that of the lens should be adjustable by a rack-work; also a swivel-mounted little mirror beneath, which is needed for minute objects to be viewed by transmitted light.
572. For dissecting and displaying small parts on the stage of the microscope, besides a thin-bladed knife, the only tools needed are a good stock of common needles of various sizes, mounted in handles, and one or more saddler's-needles, which, being triangular, may be ground to sharp edges convenient for dissection. Also a pair of delicate-pointed forceps; those with curved points used by the dentist are most convenient. A cup of clean water is indispensable, with which to moisten or wet, or in which occasionally to float delicate parts. Small flowers, buds, fruits, and seeds of dried specimens can be dissected quite as well as fresh ones. They have only to be soaked in warm or boiling water.
573. The compound microscope is rarely necessary except in cryptogamic botany and vegetable anatomy; but it is very useful and convenient, especially for the examination of pollen. To the advanced botanist it is a necessity, to all students of botany an aid and delight.
[574.] Analysis. A few directions and hints may be given. The most important is this: In studying an unknown plant, make a complete examination of all its parts, and form a clear idea of its floral structure and that of its fruit, from pericarp down to the embryo, or as far as the materials in hand allow, before taking a step toward finding out its name and relationship by means of the keys or other helps which the Manuals and Floras provide. If it is the name merely that is wanted, the shorter way is to ask some one who already knows it. To verify the points of structure one by one as they happen to occur in an artificial key, without any preparatory investigation, is a usual but is not the best nor the surest way. It is well to make drawings or outline sketches of the smaller parts, and especially diagrams of the plan of the flower, such as those of Fig. [225], [227], [241, 244], [275]-[277]. For these, cross sections of the flower-bud or flower are to be made: and longitudinal sections, such as Fig. [270]-[274], are equally important. The dissection even of small seeds is not difficult after some practice. Commonly they need to be soaked or boiled.
575. The right appreciation of characters and terms used in description needs practice and calls for judgment. Plants do not grow exactly by rule and plummet, and measurements must be taken loosely. Difference of soil and situation are responded to by considerable variations, and other divergences occur which cannot be accounted for by the surroundings, nor be anticipated in general descriptions. Annuals may be very depauperate in dry soils or seasons, or very large when particularly well nourished. Warm and arid situations promote, and wet ones are apt to diminish pubescence. Salt water causes increased succulence. The color of flowers is apt to be lighter in shade, and brighter in open and elevated situations. A color or hue not normal to the species now and then occurs, which nothing in the conditions will account for. A white-flowered variation of any other colored blossom may always be expected; this, though it may be notable, no more indicates a distinct variety of the species than an albino would a variety of the human species. The numerical plan is subject to variation in some flowers; those on the plan of five may now and then vary to four or to six. Variations of the outline or lobing of leaves are so familiar that they do not much mislead. Only wider and longer observation suffices to prevent or correct mistakes in botanical study. But the weighing of evidence and the balancing of probabilities, no less than the use of the well-ordered and logical system of classification, give as excellent training to the judgment as the search for the facts themselves does to the observing powers.
[§ 4.] SIGNS AND ABBREVIATIONS.
576. For a full account of these, whether of former or actual use, see "Structural Botany" of the "Botanical Text Book," pp. 367, 392, as also for the principles which govern the accentuation of names. It is needful here to explain only those used in the Manuals and Floras of this country, for which the present volume is an introduction and companion. They are not numerous.
577. In arranging the species, at least those of a large genus, the divisions are denoted and graduated as follows: The sign § is prefixed to sections of the highest rank: these sections when they have names affixed to them (as Prunus § Cerasus) may be called subgenera. When the divisions of a genus are not of such importance, or when divisions are made under the subgenus itself, the most comprehensive ones are marked by asterisks, * for the first, * * for the second, and so on. Subdivisions are marked with a prefixed +; those under this head with ++; and those under this with =, if there be so many grades. A similar notation is followed in the synopsis of the genera of an order.
578. The interrogation point is used in botany to indicate doubt. Thus Clematis crispa, L.? expresses a doubt whether the plant in question is really the Clematis crispa of Linnæus. Clematis? polypetala expresses a doubt whether the plant so named is really a Clematis. On the other hand the exclamation point (!) is used to denote certainty whenever there is special need to affirm this.
579. For size or height, the common signs of degrees, minutes, and seconds, have been used, thus, 1°, 2', 3", stand respectively for a foot, two inches, and three lines or twelfths of an inch. A better way, when such brevity is needed, is to write 1ft. 2in. 3l.