Root: It is the non-green underground part of the plant that anchors the plant to the soil and participates in the absorption of water and minerals. Stem: It is usually the above-ground and elevated part of the plant with side branches. The root is the non-green cylindrical shaft of the plant that usually grows down into the soil.
Tap root system: It is a mass of roots that develop from the radicle of the fetus. Deep feeder taproot system has an elongated taproot which penetrates the deeper layers of the soil. Fissure roots (Stifling roots): These are short but thick buttress roots which develop obliquely from the basal nodes of the trunk.
These adventitious roots develop from the stem of the parasite and penetrate the host where they make contact with its vascular tissue. Root thorns: In Pothos armatus and Acanthorhiza some of the secondary roots are replaced by hard, thick and pointed thorns. Anchorage: Roots take part in fixing the plant and support the aerial root system.
The axis of the plant thus formed is false because it is formed due to the fusion of the basal part of successive lateral branches and called as sympodia axis.
Upright weak Stems: They are of two kinds, twiners and climbers
They are of three types - reduced, elevated and weak. A) Reduced stem: The stem is reduced to a small disk. Such a green discoid stem appears in the vegetative phase above the base of the root in radish, carrot, turnip, etc. They are small long runners of one internode found on rosette plants at soil or water level, e.g.
It grows horizontally on the ground and at the underground base of an erect shoot or crown. It grows horizontally on the ground and eventually emerges to form a new aerial stem or crown. Although mistakenly known as rootstocks, rhizomes are strictly stems in the sense that they bear nodes and internodes.
In the tunicate bulb, the scale leaves overlap each other with a dry scale called the tunic on the outer side. The bulb is called simple tunicate or layered when the leaves of the scales are arranged concentrically and form a series of rings. A canopy can be a modification of a stem, branch, leaf or part of a leaf. a) Traces of axillary branches: Found in Passiflora.
Their axillary position, branching structure and presence of flaky leaves and buds on them confirm their stem structure. In Antigonon the flowers occur in branches in the axils of shield leaves on the flower shoot. In Opuntia (vern. Chittarthor) the stem is green and leafy, it is oblate, fleshy, thick, connected structure appearing in the axil of caducous leaf at node.
They are borne in the axils of scaly or spiny leaves at nodes or normal stems. They also perform photosynthesis in the absence of leaves that are modified into scales or spines. In Ruscus, cladodes are green, leathery, flattened, leaf-like structures located singly in the axils of scale leaves.
Primary or main functions
Secondary or Accessory functions
MORPHOLOGY OF LEAF
Lamina (=epipodium) or leaf blade is the terminal thin, expanded, green and conspicuous part of the leaf, which is specialized to carry out photosynthesis. The flattened lamina or leaf blade is supported by veins and veins which contain vascular tissue. Petiole (=mesopodium) is a cylindrical or subcylindrical petiole of the leaf which raises the lamina above the level of the stem to give it maximum exposure.
Leaf base (=hypopodium) is the lower part of the leaf, by which the leaf is connected to the node of the stem. The latter are of two types - amplexicaul (enclosing the stem completely as in Grasses, Wheat) and semi-amplexicaul (enclosing the stem partially, e.g. Buttercup). A leaf with stipules is called stipulated, while one without stipules is called exstipulate.
They are two small lateral outgrowths of the base of the leaf which protect the young leaf and its axillary bud in the young state. Shoe flower (Hibiscus rosa-sinensis). ii) Scaly: Very small dry membranous stipules, e.g. iii) Axillary or intrapetiolar: Stipules are fused from their inner margins to become axillary. iv) Opposite: Stipules are fused from their outer margins to be opposite the leaf. Castor (v) Interpetiolar: Adjacent stipules of opposite leaves are fused to emerge between the leaves. vi) Adnate or petiolar: Stipules fused with petiole, e.g. vii) Ocreate: Stipules fuse together to form a sheath or ocrea around the stem, e.g. viii).
The purpose of phyllotaxy is to orient the leaves in such a way that they receive maximum sunlight to perform the function of photosynthesis. Alternate or spiral: When only one leaf is borne at each node, the arrangement is called spiral or alternate or acyclic.
Reproductive leaf: Leaves of Bryophyllum and Begonia bear adventitious buds on them and help in vegetative propagation of plants
In Eucalyptus and Soncus, the leaves differ in shape and size, having appeared in different developmental periods of the same plant. Lal Patti), the leaves near the cyathia are brightly colored to attract pollinating insects. they are brightly colored to attract pollinating insects. Sheet insertion is of three types: i) Radical: Leaves resting on a reduced disc stem and appearing to rise in clusters from the apex of the root. ii) Stem: Leaves located at the nodes of the stem (or main stem). iii) Ramal: Leaves at the nodes of the stem branches. i) Caducous: Leaves fall soon after bud opening. ii) Deciduous: all the leaves of the plant fall one after another at the end of the growing season or the plant remains leafless at the same time. iii) Persistent: The leaves do not fall at the same time and the plant is never leafless.
A leaf with a petiole attached posteriorly to the middle of the lamina. v) Inflated or spongy: The stem is bulbous, swollen and holds air. you). The leaf is long, narrow, cylindrical, needle-like with a sharp tip. ii) Linear: The lamina is long, narrow and flat with almost uniform width. It is widest in the middle but tapers at both ends. vi) Ovate: The lamina has a broadly rounded base and a sharp or blunt tapering tip.
The tip forms an obtuse angle. iv) Cuspidate or spinose: The tip is in the form of a long stiff pointed tip. Tendrillar: Apex forms sensitive, coiled appendages called tendrils. vii) Cut: The tip ends abruptly and appears to be cut at right angles to the midrib. Pigments block light energy and convert it into chemical energy which is used in the synthesis of organic food.
Transpiration is helpful in the emergence of sap and keeps the temperature low in summers. The vascular elements in the veins and petioles help in the conduction and transport of water and minerals from the stem to the lamina and organic food from the lamina to the stem.
Secondary or special functions
The surface is covered with dense or sparse hairs. vi) Pilose: Surface sparsely covered with long soft and slender hairs. vii) Hirsute: Surface covered with coarse and stiff hairs. viii). Tomentose: Surface densely covered with short woolly hairs forming a mat. ix) Hispid: Surface surrounded with stiff or bristly hairs. The most important primary function of leaf is the production of organic food through photosynthesis.
Any peculiarity of shape, size, color, including variation of leaves, is picked up by horticulturists for propagation.
Angiosperms: Origin And Evolution
Campbell also pointed out the marked similarity in habit and similarities in the embryo and anatomy of the parent sporophyte between Isoetales and some other lower aquatic monocots. He suggested that the carpel wall of angiosperms may represent some concretion cups and that the possible origin of the stigma should be considered in the light of these ancient forms. The only difference between primitive monocots and Nymphaeales is the presence of two cotyledons in the latter.
This group of plants dominated the earth in the distant past during the Late Paleozoic and Mesozoic. The fossil was first discovered in the form of compression from the Upper Devonian strata of eastern North America. The second form genus Callixylon was found in the form of petrified fossils from the same age and locality.
The extinct breadfruit-like plants are included in the group Cycadeoidales (Bennettiales) showing close affinities with breadfruits as well as the angiosperms. The cycadeoids occupy the terminal position in the line of gymnosperm evolution and due to the presence of peculiar hermaphrodite flowers such as strobilii, they are considered to be forerunners of the modern angiosperms (Crane, 1988, Doyle and Donoghue, 1987). Generally, the leaf spurs originate in stems until the formation of leaf gaps just above the starting points of leaf spurs.
A brief outline of these is given below:. i) The primitive stele is protostele consisting of a central solid core of xylem surrounded by phloem. The ribs present in the protoset represent the point of. origin of radially divergent leaf spores. In the next stage; the central longitudinal column is dissected into three or more longitudinal columns with the origin of parenchymatous marrow in the central region (i.e., medullation).
The longitudinal columns move more towards the circumference due to the appearance of massive pith in the middle. This type of vascular system is found in the main axis of the leaf of Archaeopteris, Calamopits, etc. iv). The next step of evolution is the change in the nature of division of sympodial bundle.
The reduction in the number of megaspores, along with some other changes in the megasporangium, must have occurred at the origin of the preovule and finally to the ovule and seed. Some important evolutionary events in the origin and development of the ovule may be as follows: i) Reduction of the number of functional megaspores to one in each megasporangium. ii) Retention of megaspores in megasporangium.
