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.