A British systematic botanist J. Hutchinson published his work, The Families of Flowering Plants in 1926 on dicotyle-dons and in 1934 on monocotyledons. Hutchinson made it clear that the plants with sepals and petals are more primitive than the plants without petals and sepals on the assumption that free parts are more primitive than fused ones.
Study of
Different Families
INTRODUCTION
A British systematic botanist J. Hutchinson published his
work, The Families of Flowering Plants
in 1926 on dicotyle-dons and in 1934 on monocotyledons. Hutchinson made it
clear that the plants with sepals and petals are more primitive than the plants
without petals and sepals on the assumption that free parts are more primitive
than fused ones. He also believed that spiral arrangement of floral parts,
numerous free stamens and hermaphrodite flowers are more primitive than
unisexual flowers with fused stamens. He considered monochlamydous plants as
more advanced than dicotyledons. Hutchinson’s system indicates the concept of
phylogenetic classification and seems to be an advanced step over the Bentham
and Hooker system of classification. Hutchinson accepted the older view of
woody and herbaceous plants, and fundamentally called them as Lignosae and
Herbaceae. He revised the scheme of classification in 1959. He has divided the
flowering plants into two phyla: phylum I—Gymnospermae (not elaborated by him)
and phylum II—Angiospermae. The latter are divided into two sub-phyla:
sub-phylum I—Dicotyledons and sub-phylum II—Monocotyledons.
The division of angiosperms into these two large classes is
based on the following factors:
1) In dicotyledons, the embryo bears
two cotyledons, and in monocotyledons, it bears only one.
2) In dicotyledons, the primary root
persists and gives rise to the tap root, while in monocotyledons, the primary
root soon perishes and is replaced by a cluster of adventitious (fibrous)
roots.
3) As a rule, venation is reticulate in
dicotyledons and parallel in monocotyledons. Among monocotyledons, aroids,
sarsaparilla (Smilax) and yams (Dioscorea), however, show reticulate
venation, and among dicoty-ledons, Alexandrian laurel (Calophyllum) shows parallel venation. Further, in dicotyledons,
the veinlets end freely in the mesophyll of the leaf, whereas in
mono-cotyledons, veins or veinlets do not end freely.
4) The dicotyledonous flower usually
has a pentamerous symmetry, sometimes tetramerous (as in Cruciferae and Rubiaceae),
while the monocotyledonous flower has a trimerous symmetry.
5) In the dicotyledonous stem, the
vascular bundles are arranged in a ring and are collateral and open, i.e. they
contain a strip of cambium which gives rise to secondary growth. In the monocotyledonous
stem, however, the bundles are scattered in the ground tissue and are
collateral and closed. Hence, there
is no secondary growth (with but few exceptions). Also the bundles are more
numerous in monocotyledons than in dicotyledons. Further, they are more or less
oval in monocotyledons and wedge shaped in dicotyledons.
6) In the dicotyledonous root, the
number of xylem bundles varies from 2 to 6, seldom more, but in the
monocotyledonous root there are many, seldom a limited number (5–8). It may also
be noted that the cambium soon makes its appearance in the dicotyle-donous root
as a secondary meristem and gives rise to secondary growth, but in the
monocotyledonous root, the presence of cambium is rare. Hence, there is no
secondary growth.
Floral Diagram
The number of parts of a flower, their general structure,
arrangement and the relation they bear to one another (aestivation), adhesion,
cohesion, and position with respect to the mother axis may be represented by a
diagram known as the floral diagram. The floral diagram is the ground plan of a
flower. In the diagram, the calyx lies outermost, the corolla internal to the
calyx, the androecium in the middle, and the gynoecium in the centre. Adhesion
and cohesion of members of different whorls may also be shown clearly by
connecting the respective parts with lines. The black dot on the top represents
the position of the mother axis (not the pedicel), which bears the flower. The
axis lies behind the flower and, therefore, the side of the flower nearest to
the axis is called the posterior side, and the other side away from the axis
the anterior side. The floral characteristics of species may be well
represented by a floral diagram, whereas more than one diagram may be necessary
to represent a genus or family.
Floral Formula
The different whorls of a flower, their number, cohesion and
adhesion may be represented by a formula known as the floral formula. In the
floral formula, K stands for calyx, C for corolla, P for perianth, A for
androecium and G for gynoecium. The figures following the letters K, C, P, A
and G indicate the number of parts of those whorls. Cohesion of a whorl is
shown by enclosing the figure within brackets, and adhesion is shown by a line
drawn on top of the two whorls concerned. In the case of the gynoecium, the
position of the ovary is shown by a line drawn above or below G on the figure.
If the ovary is superior, the line should be below it; and if inferior, the
line should be on top. Thus, all the parts of a flower are represented in a
general way by a floral formula.
Besides, some symbols are used to represent certain features
of flowers. Thus ♂ represents male, ♀ female, H hermaphrodite, ♂♀ dioecious,
♂-♀ monoecious, ♂ ♀ H polygamous, ⊕ actinomorphic, ·׀·zygomorphic, ∞ indefinite number of
parts, etc.
Features used in descriptions of Angiospermic plants:
· Habitat: Natural abode of the plant.
· Habit: Herb (erect, prostrate,
decumbent, diffuse, trailing, twining or climbing), shrub (erect, straggling,
twining or climbing), tree or any other peculiarity in the habit.
· Root: Nature of the foot; any
special form.
· Stem: Kind of stem—herbaceous or
woody; cylindrical or angular; hairy or smooth; jointed or not; hollow or
solid; erect, prostrate, twining or climbing; nature of modification, if any.
· Leaf: Arrangement—whether alternate,
opposite (super-posed or decussate) or whorled; stipulate or exstipulate;
nature of the stipules, if present, simple or compound; nature of the compound
leaf and the number of leaflets; shape and size; hairy or smooth; deciduous or
persistent: venation; margin; apex; and petiole.
· Inflorescence: type of
inflorescence.
· Flower: sessile or stalked; complete
or incomplete; unisexual or bisexual; regular, zygomorphic, or irregu-lar;
hypogynous, epigynous or perigynous; bracteate or ebracteate; nature of bracts
and bracteoles, if present; shape, colour and size of the flower.
· Calyx: polysepalous or gamosepalous;
number of sepals or lobes; superior or inferior; aestivation; shape, size and
colour.
· Corolla: polypetalous or
gamopetalous; number of petals or lobes; superior or inferior; aestivation;
shape, size colour and scent; corona or any special feature. (When there is not
much difference between the calyx and the corolla, the term perianth should be
used. It may be sepaloid or petaloid, polyphyllous or gamophyllous, or free or
epiphyllous).
· Androecium: number of
stamens—definite (10 or less) or indefinite (more than 10); free or united;
nature of cohesion—monadelphous, diadelphous, polyadelphous, syngenesious or synandrous;
nature of adhesion—epi-petalous or gynandrous, or any special feature; whether
alternating with the petals (or corolla lobes) or opposite them. Length of
stamens—general length; inserted or exerted; didynamous or tetradynamous;
position of stamens—hypogynous, perigynous or epigynous; attach-ment of the
anther and its dehiscence; anther lobes or appendages, if any,
· Gynoecium or pistil: number of
carpels; syncarpous or apocarpous; nature of style—long or short; stigmas—
simple, lobed or branched; their number and nature— smooth or papillose;
ovary—superior or inferior; number of lobes; number of chambers (loculi);
nature of pla-centation; number and form of ovules in each loculus of the
ovary.
· Fruit: kind of fruit.
· Seeds: number of seeds in the fruit;
shape and size; albuminous or exalbuminous; nature of endosperm, if present.
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