ctice 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.

Sec. 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 Sec. is prefixed
to sections of the highest rank: these sections when they have names
affixed to them (as Prunus Sec. 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