Structure of roots, stems, leaves, flowers, fruits and seeds of plants

1. Root tip structure

The part from the top of the root to the root hair is called the root tip, which consists of root cap, growth point (also called meristem area), elongation area and root hair area (also called mature area). Because these four parts are introduced in detail in junior high school textbooks, I won't repeat them here.

2. Primary structure of roots

On the cross section of the root hair area or above, the epidermis, cortex and stele are in turn from outside to inside. Because they are all formed by the growth and differentiation of the primary meristem of roots, they are called the primary structure of roots.

(1) Epidermis: Around the outermost layer of the root, the cells are approximately rectangular and cylindrical, the long diameter is parallel to the longitudinal axis of the root, the cell wall is thin, there are large vacuoles, and they are arranged neatly without intercellular gaps, and some epidermal cells form root hairs. The epidermis has absorption and protection.

(2) Cortex: Located between epidermis and stele, it is generally composed of multiple layers of large parenchyma cells. In the root structure, the cortex is large, loosely arranged, and the cell gap is large. Its function is to transport water and inorganic salts absorbed by epidermis to the middle column; At the same time, organic nutrients in the middle column are transported out. In addition, cortical cells often contain many starch granules and other nutrients, so the cortex also has storage function.

The innermost cell of the cortex, that is, the cell next to the stele, is called the endodermis. The cells are closely arranged, and there is no intercellular space. Its main feature is that the cell wall is thickened in a special way, one of which is that the radial wall and transverse wall of each cell are locally thickened into bands and embolized. This special structure around cells is called Kjeldahl zone. Another thickening method is that the radial wall, transverse wall and tangential wall (the side facing the vascular column) of most endothelial cells are obviously thickened and embolized, but only the tangential wall is not thickened. Seen from the cross section, the thickened cell wall of the endodermis is horseshoe-shaped, thus losing the ability of water permeability and ventilation. However, a few cells remain thin-walled and become channels for internal and external communication of water and nutrients. The special thickening of the cell wall of the endodermis is of great significance for controlling the direction of root sap flow. The structure of the endodermis is shown in the following figure.

3. Formation of lateral roots

The lateral roots of seed plants come from columnar sheath cells in the main roots, which are endogenous. The generation of lateral roots on the pericycle sheath often has a certain position. Usually, lateral roots can only be produced in pericycle cells opposite to the radiation edge of primary xylem. Therefore, you can see that there are the same number of predictions vertically arranged on the periphery of the root about the radiation edge of the primary xylem in the root. For example, the root of broad bean has four primary xylem radiation edges, and the main root has four rows of lateral roots. But in some plants, the number of rows of lateral roots can be multiple of the primary xylem ridge. In addition, there are a few plants, such as many Gramineae plants, whose lateral roots occur in the pericycle sheath opposite to the primary phloem.

4. The secondary structure of roots

Most monocotyledonous plants and a few dicotyledonous plants have short root life, and the primary structure of the root is maintained until the plant dies without thickening. The roots of most dicotyledonous plants and gymnosperms, especially the roots of perennial woody plants, produce various secondary tissue after primary growth, which makes the root diameter thicker year by year. This growth mode is called secondary growth. The tissues and structures produced by secondary growth are called secondary structures.

(1) Occurrence and activity of cambium: The cambium of roots is formed by the restoration of meristematic ability of parenchyma cells between primary xylem and primary phloem. The cambium begins with a few parenchyma cells in the primary phloem, and then gradually expands to the left and right sides, and moves outward to the stele sheath. At this time, some cells located at the top of the primary xylem bundle also recovered their meristematic ability. Results A wavy cambium ring was formed between primary xylem and primary phloem. After that, all cells divide at different speeds, and the cambium cells in the primary phloem divide rapidly, forming more secondary xylem. However, the cambium cells outside the radiation edge of the primary xylem divide slowly, thus changing the original wavy cambium ring into a neat ring. After that, the division of cambium cells is basically at the same speed, so the root thickening is uniform. In addition to continuous centriole division, cambium cells also produce secondary phloem outward and secondary xylem inward, and at the same time, they also divide vertically to expand the circumference.

The composition of secondary xylem and secondary phloem is basically the same as that of primary xylem and primary phloem. However, some radial parenchyma cells, called vascular rays, are often produced in the secondary structure, which cross between the secondary xylem and the secondary phloem and have the functions of storing nutrients and transporting nutrients horizontally.

(2) The occurrence and activity of wood column cambium: During the secondary growth of cambium, the cortex and epidermis outside the stele sheath burst due to the continuous expansion of stele. At the same time, the parenchyma cells of the stele sheath recovered their meristematic ability and formed the cambium of the wood column. The activity of the cambium of the wood column is similar to that of the cambium, and it is also divided horizontally, and new cells are constantly produced from the inside out. The tissue produced outward is called cork, and several layers of parenchyma cells formed inward are called cork inner layer. The wooden column consists of multiple layers of radially arranged, compact and tidy cells. After the cell matures, the cell wall becomes embolic, the protoplasts disintegrate, and the dead cells are filled with air. The cork layer is isolated from the connection between the cortex and the stele and the circulation of substances because of the thickening of the cell wall, so when the cork is formed, the tissues around the stele die because of the cut-off of nutrient supply. Periderm is composed of cork, wood column cambium and inner layer, which replaces the original epidermis to exercise protective function. The occurrence and activity of root cambium are shown in the following figure.

A B C D

Schematic diagram of each stage of root cambium formation

A. cambium has not yet occurred. Cambium fragments have occurred.

C. the cambium is wavy. The cambium is round.

(3) the structure of the stem

The stem structure of dicotyledonous plants and monocotyledonous plants is different in tissue arrangement, as shown in the following figure.

1. Primary structure of dicotyledonous stems

This structure is a variety of tissues formed by cell division, growth and differentiation of meristem at the top of stem. Like the primary structure of roots, they are also divided into epidermis, cortex and stele.

(1) Epidermis: It is usually composed of a layer of flat cells, with regular cell shapes, tight arrangement and no cell gaps. The outer wall of epidermal cells is often thickened, and the surface often has cuticle and epidermis, and some are waxy. These structures have the function of strengthening protection.

Cross-sectional view of stem of dicotyledonous and monocotyledonous plants

(2) Cortex: The epidermis is cortex, consisting of multiple layers of parenchyma cells. However, it is generally not as developed as the cortex of roots, and there are obvious intercellular spaces. Thin-walled cells near the outside usually contain chloroplasts, so young stems are usually green. The cortex of the stem often has thick horny tissue, which appears in bundles to make the stem prismatic, such as labiatae plants; Or connected into a cylinder around the inside of epidermis, such as Cucurbitaceae; Other plants have fibers or stone cells in their cortex. In the stems of some herbs (such as pumpkin and broad bean), there are many starch grains in the innermost layer of cortex, which are called starch sheaths.

(3) Vascular column: The vascular column of dicotyledonous stems is all tissues in the cortex, including primary vascular bundles, pith and pith rays.

The most important part of the vascular column is the primary vascular bundle, which often exists in bundles and is arranged in a ring. Each paper bundle consists of primary phloem, cambium and primary essence. Most of them are the arrangement of primary phloem on the outside and primary xylem on the inside, that is, primary xylem and primary phloem are juxtaposed inside and outside (called lateral vascular bundles), such as sunflower, castor and alfalfa. The arrangement of primary xylem in stem sandwiched between inner phloem and outer phloem is called double tough vascular bundle. These vascular bundles are common in the stems of Cucurbitaceae (Cucurbitaceae), Convolvulaceae (Sweet Potato), Solanaceae (Tomato), Apocynaceae (Nerium indicum) and other plants, among which Cucurbitaceae stems are typical. In the double tough vascular bundle, there is no cambium between the inner phloem and the primary xylem, or the cambium is very weak. Zhou Ren paper bundles are arranged with xylem at the center and phloem at the periphery. Perivascular bundles usually exist in the stems of algae, but are rare in angiosperms, such as the vascular bundles in the stems of rhubarb, Rumex and other plants. The vascular bundles of some dicotyledonous plants are also perifascicles. Zhou Muwei's vascular bundle is arranged with phloem in the middle and xylem outside. Zhou Muwei bundle exists in both monocotyledonous and dicotyledonous plants. The former is the vascular bundle in the underground stems of Typha Typha, Iris, Cyperus and Lily of the Valley, while the latter is the vascular bundle in some stems of Leguminosae and Zanthoxylum. It is worth noting that there are two types of vascular bundles in the stems of plants, such as the stems of monocotyledonous plant Dracaena. The primary vascular bundle is lateral vascular bundle, and the secondary vascular bundle is Zhou Muwei bundle. As shown in the figure below.

The cross section of the stem of Dracaena Dracaena shows secondary thickening.

A. There are only primary vascular bundles in the stem. Secondary vascular bundles have been formed in the stem. The cross section of a part of the stem shows the secondary circumferential wood bundle.

1 .cortex 2. Primary vascular bundle 3. Secondary vascular bundle 4. Cambium 5. Zhou muwei tied up

The primary phloem of dicotyledonous plants consists of sieve tubes, companion cells, parenchyma cells and phloem fibers. The development sequence of primary phloem is the same as that of root, and it is also exogenous, that is, the primary phloem is on the outside and the later phloem is on the inside; Primary xylem consists of vessels, tracheids, parenchyma cells and lignocellulose. Their developmental sequence is internal, which is contrary to the external development of primary xylem in roots. The protoxylem in the stem is located at the inner side, and consists of a ring-shaped or threaded catheter with a smaller diameter. Metamorphic xylem is located outside and consists of large-diameter ladder-shaped, reticulated and striated vessels. There is cambium between primary xylem and primary phloem.

The pith is located in the center of the stem and usually consists of parenchyma cells and intercellular spaces. In the process of stem growth of some plants, the central part of pith is destroyed and disappears, forming pith cavity. Herbs are usually like this. Myeloid rays, also known as primary rays, are located between vascular bundles and consist of parenchyma cells. Radial arrangement in cross section, the lateral side is connected with cortex, and the medial side is connected with bone marrow. Its function is mainly to carry out the task of lateral transportation, and it has the function of storage.

2. The secondary structure of dicotyledonous stems

The secondary structure of dicotyledonous stems began to appear shortly after the formation of primary structure.

The formation of secondary structure of stem, like root, is also the result of cambium and cork cambium activities.

(1) cambium activity and formation of secondary vascular tissue: The primary meristem of dicotyledonous plants is not fully mature in the process of forming vascular bundles, but a layer of meristem remains between primary xylem and primary phloem, which becomes cambium in Cambodia. When the secondary growth of the stem began, the cambium in the bundle began to split, and the myeloid ray cells equivalent to the cambium in the bundle also recovered their meristematic ability to form the cambium between bundles. As a result, the bundle connects with the cambium between the bundles to form a cylinder, and then starts to move. The main activity mode of cambium cell area is tangential division, which produces new cell layers inward and outward. The cells in each layer are evenly arranged radially, and further differentiate inward to form secondary xylem, which is added to the outside of primary xylem; The secondary phloem forms outward and attaches to the inner side of the primary phloem. The cambium continuously divides tangentially to form a secondary structure, and at the same time, it also splits horizontally and radially to expand the circumference of the cambium to adapt to the increase of internal xylem. At the same time, its position gradually moved outward, which eventually led to the increase of rent and the elongation of stems. Specific as shown in the figure below.

Activity diagram of cambium cells

During the formation of secondary xylem and secondary phloem, some cells in cambium extend radially to form vascular rays.

(2) Activity of cork cambium: Most cork cambium in stem is formed by restoring the division ability of cortical parenchyma cells near epidermis, but a few are transformed from phloem parenchyma cells. Its activity is similar to that in roots, mainly horizontal division, outward formation of cork, inward formation of cork inner layer cells (a small amount). In the process of cork formation, there will be some light brown round, oval or even long protrusions on the surface of branches, which are called lenticels. Periderm is a ventilation structure on the periderm, which is a living cell located in the periderm. The stem exchanges gas with the outside world through the lenticels.

Cork, cork cambium and cork inner layer are collectively called periderm. The formation process of periderm is shown in the following figure.

Formation of peristemic skin

Pay attention to distinguish between cells in the inner layer of cork and cortical cells. The inner layer of cork is also a thin-walled living cell, often only one layer thick. Generally, cortical parenchyma cells can only be distinguished from cortical parenchyma cells by arranging them on the same neat radial line with cork cells outside.

To sum up, compared with roots, the secondary xylem of stems has many similarities, that is, not only the composition is the same, but also the arrangement and proportion of xylem and phloem are similar, and even the place where cork cambium occurs is not different in older materials, and it is formed by the secondary phloem in the later period. The difference is that the root has an external primary xylem in the center, while the stem has a pith in the center, and the periphery of the pith is an internal primary xylem.

(3) Seasonal activities of vascular cambium and formation of annual rings: The activities of vascular cambium are greatly influenced by seasons, especially in temperate and subtropical regions with obvious cold and warm seasons, or tropical regions with clear dry and wet seasons. The activity of vascular cambium changes rhythmically with the change of seasons, which leads to more or less cells, large or small shapes, and thick or thin cell walls. Because the secondary xylem accounts for a large proportion in the stems of perennial woody plants, its morphological structure is significantly different in different seasons and different periods. In temperate spring or tropical wet season, due to high temperature and sufficient water, cambium activity is vigorous, and in the secondary xylem formed, cells are large and thin, with few fibers; In temperate zone in late summer and early autumn or tropical dry season, cambium activity is weakened. In the secondary xylem formed, cells are small and thick, tracheids often increase, and lignocellulose components increase. The former is formed in the early growing season, called early wood or spring wood, and the latter is formed in the late growing season, called late wood or summer wood or autumn wood. From the cross section, the early wood grain was loose and slightly pale in color; Late wood is dense in texture and dark in color. From early wood to late wood, it changes gradually with the seasons. Although you can see the difference between color and texture, there is no clear boundary. However, we can see a very obvious boundary between the late wood of last year and the early wood of that year, because the shape, size and wall thickness of the two cells are very different. In a growing season, early wood and late wood form a remarkable concentric ring layer, which represents the secondary xylem formed in a year. In areas with significant seasonal climate, the secondary wood of many plants forms an annual ring under normal circumstances, which is customarily called annual ring. However, there are also many plants that form more than one annual ring in a year's normal growth. For example, the stem of citrus plants will produce three annual rings in a year, and only three annual rings can represent the growth of a year, so it is called fake annual rings. The formation of false annual rings is also due to the special change of climate in that year or the inhibition of plant growth after pests harm leaves.

3. Stem structure of monocotyledonous plants

The stem structure of monocotyledons is obviously different from that of common dicotyledons:

(1) Most monocotyledonous plants, like their roots, have no cambium, so they have only primary structure and no secondary structure.

② The vascular bundles in the stem of dicotyledonous plants are arranged in a wheel shape, so the cortex, pith and pith rays are clearly defined. The vascular bundles in the stem of monocotyledonous plants are scattered in the basic tissues, so there is no boundary between cortex and pith, and the rays cannot be clearly distinguished.

Among monocotyledonous plants, there are also a few species, such as Dracaena, bamboo, Phyllostachys pubescens, aloe, etc., which have cambium in their stems, so they have secondary growth and secondary structure. However, the origin and activities of their cambium are quite different from those of dicotyledonous plants. For example, the cambium in Longxue Village is not in the vascular bundle, but in the parenchyma cells outside the vascular bundle.

4. Stem structure of gymnosperms

The stem of gymnosperms is similar to the woody stems of dicotyledonous plants, and its primary structure consists of epidermis, cortex and vascular column. The secondary structure consists of secondary phloem and secondary xylem, which can form annual rings, early wood and late wood. Periderm is produced by the cambium of wooden pillars. There are also many differences between gymnosperms and dicotyledons: there are no conduits and wood fibers in the axis system of gymnosperms, but tracheids bear the dual functions of transporting water, inorganic salts and supporting. Therefore, compared with dicotyledonous plants, the secondary xylem structure in gymnosperms stems appears uniform and tidy; The secondary phloem of gymnosperms has sieve cells, no sieve tubes and companion cells, and some gymnosperms also have no phloem fibers. Gymnosperms have many resin channels. Resin channels are distributed in cortex, phloem, xylem, pulp and even medullary rays. Resin duct is usually a secretory duct surrounded by two layers of cells.

(4) Blade structure

General structure of angiosperm leaves

The leaves of angiosperms generally have different upper and lower surfaces. The upper surface (ventral surface or paraxial surface) is dark green, while the lower surface (dorsal surface or paraxial surface) is light green. This kind of leaf is due to the lateral position of the leaf on the branch, almost perpendicular to the long axis of technology or parallel to the ground, and the two sides of the leaf receive different light, so the internal structure of the two sides is also different, that is, the tissues that make up mesophyll are greatly differentiated, forming fence tissues and sponge tissues. The leaves of some plants are almost upright, almost parallel to the long axis of branches or perpendicular to the ground. There is little difference between the two sides of the leaf, so the internal structure of the two sides of the leaf is similar, that is, the tissue that makes up the mesophyll has little differentiation, and this kind of leaf is called equivalent surface leaf. Some plants also have palisade tissue in the upper and lower leaves, and sponge tissue in the middle, also known as equilateral leaves. As far as leaves are concerned, they are all composed of epidermis, mesophyll and veins.

Epidermis: covering the whole leaf, with upper and lower epidermis. The epidermis usually consists of a layer of living cells, but there are also many layers of cells, which are called compound epidermis, such as the epidermis of oleander and Indian rubber leaves. There are pores on the epidermis, and there are four main types of pores: irregular, nonlinear, parallel and horizontal. The number and distribution of stomata in leaves of various plants are different. The stomata in the upper leaves of plants are more than those in the lower leaves, and the stomata in the top and midvein of leaves are greener than those in the base and leaves. Some plants, such as sunflower, castor, corn, wheat, etc., have stomata on the upper and lower epidermis, and the lower epidermis is generally more. However, the stomata of some plants are only limited to the lower epidermis (such as early lotus and apple) or the upper epidermis (such as water lily and lotus flower), and the stomata of some plants are only limited to the local area of the lower epidermis, such as the stomata of oleander leaves only born in concave stomata nests. In different external environments, the number of stomata in the same plant leaves is also different. Generally, there are many sunny places and few wet places. The leaves of submerged plants generally have no stomata (such as POTAMOGETON POTAMOGETON).

The structure of mesophyll and vein is introduced in detail in junior high school textbooks, so I won't go into details here.

2. Leaf structure of Gramineae plants

The basic structure of leaves of Gramineae plants also includes epidermis, mesophyll and veins, but it has the following characteristics: the epidermis of leaves is composed of a layer of orderly and slightly rectangular epidermal cells, and the outer walls of epidermal cells are not only keratinized but also filled with silica, and some even pile up into rough protrusions. There are also some special large vacuoles, and there are large vacuoles in the upper epidermis of leaves, which are arranged in a fan shape or moving cells. They are located between two adjacent veins, which are related to the unfolding and curling of leaves and can control the transpiration of water. There are more stomata in the upper epidermis than in the lower epidermis, and the stomata are composed of two dumbbell-shaped guard cells, and there is a secondary guard cell similar to a long spindle on the outside of each guard cell. There is no obvious difference between palisade tissue and sponge tissue in mesophyll tissue, and the structure is uniform, which is composed of some short-axis parenchyma cells. Veins are arranged in parallel, and there are developed mechanical tissues between vascular bundles and upper and lower epidermis. Each vascular bundle is surrounded by a vascular bundle sheath consisting of one or two layers of large parenchyma cells. The outer cells of vascular bundle sheaths such as rice, barley and wheat have large thin walls and fewer chloroplasts than mesophyll cells. The inner layer is thick-walled, with small cells and almost no chloroplasts. However, the veins of rice generally have only one vascular sheath. The vascular bundle sheaths of leaves of plants such as maize are well developed, containing large chloroplasts, and a circle of mesophyll cells is close to the outside, forming a "garland" structure. This "garland" anatomical structure is the characteristic of C4 plants. The leaves of wheat and rice have no "garland" structure, and chloroplasts in vascular bundle sheath cells are less than mesophyll cells. This is the characteristic of C3 plant leaves.

3. The structure of needles in gymnosperms

There are many types of leaves in gymnosperms, such as needles, strip leaves, spiny leaves, scale leaves and fan leaves, among which needles are found in Pinaceae. Needle structure is dry, with small surface area, thick epidermal cell wall, strong lignification and covered by thick cuticle. Stomatal subsidence is often blocked by resin in winter, thus reducing transpiration. There are one or several layers of thick-walled cells under the epidermis, called the subcortical layer, which plays a supporting role. The cell wall of mesophyll cells protrudes inward, expanding the photosynthetic area. There are resin channels in mesophyll, and the interior of mesophyll is endodermis. The endodermis consists of a layer of oval cells with neatly arranged corks on the side wall. In the endodermis are metastatic tissues and 1 or 2 vascular bundles. The transport tissue consists of tracheids and parenchyma cells, which are the characteristics of conifers and cypresses, and its function is to transport mesophyll and vascular bundles horizontally.

(5) Anatomical structure of flowers

A typical angiosperm flower consists of calyx, corolla, stamen and pistil.

Flowers with the above four parts are called complete flowers, such as peaches and plums. Flowers lacking some of them are called incomplete flowers, such as mulberry and beech. From the evolutionary point of view, flowers are actually deformed short branches adapted to reproduction, while calyx, corolla, stamen and pistil are deformed leaves.

1. Pedicel and receptacle

Pedicel (stem) is the connecting part between flower and stem, which mainly plays a supporting and guiding role. At the top of the pedicel is a receptacle with flowers. The shape of the receptacle varies with different plant species, such as the receptacle of Magnolia grandiflora is conical, and the receptacle of Rosa multiflora is cup-shaped.

2. Perianth

Perianth is the general name of calyx and corolla.

(1) calyx

Located outside a flower, it usually consists of several sepals. Some plants have two calyxes, and the outermost calyx is the accessory calyx, such as hibiscus and hibiscus. Calyx shedding with flowers is called caducous calyx, such as peach and plum; The remaining calyx when the fruit is ripe is called persistent calyx, such as pomegranate and persimmon. Sepals that are completely separated are called sepals, such as magnolia and Ranunculus. The calyx connected into a whole is called calyx, such as Dianthus.

(2) Corolla

Located in the calyx, it is composed of several petals arranged in one or several rounds, which has a protective effect on stamens. Because the petals contain pigments, they can secrete aromatic oil and honey juice, and the corolla is colorful and fragrant, which can attract insects and play a role in pollination.

3. Stamens

Stamens, located in the corolla, are one of the important components of flowers and consist of filaments and anthers. Filaments are slender, one end is born on the receptacle and the other end is connected with the anther, which has the function of transporting and supporting the anther. Anthers are swollen and cystic, located at the top of filaments, and usually divided into two anthers, each with one or two pollen sacs. When the pollen matures, the pollen sac cracks and a large number of pollen grains are scattered.

All the stamens in a flower form a stamen group, and the number of stamens varies with plant species. For example, Orchidaceae has only one stamen, Oleaceae has two stamens, Papilionidae has 10 stamens, and peach blossom has many stamens, but there is no definite number. According to the number of stamens and the clutch between filaments and anthers, stamens can be divided into free stamens and syncytial stamens (as shown in the figure below).

Stamen monomer polysaccharide

Tetrahedral stamens, dimorphic stamens, polygamous stamens

(Anthers are connected and filaments are separated around the lower part of the style)

Types of stamens

(1) free stamens

Stamens in flowers are separated, and there are the following kinds:

Stamen dysplasia: flowers have four stamens, two long and two short, such as Lingxiao and Paulownia.

Tetrahedral stamens: 6 stamens, four long and two short, such as cruciferous plants.

(2) Syngamous stamens

All or part of the stamens of flowers are connate, and there are the following types:

Monostamen: the lower part of the filament is connected into a tube, while the upper part of the filament is still separated from the anther, such as hibiscus, hibiscus, etc.

Diploid stamens: filaments are connected into two groups, for example, some leguminous plants have 10 stamens, of which 9 filaments are connected together and the other is separated, such as broad beans.

Polyploid stamens: filaments combine at the base to form several bundles, such as Hypericum, silver tree, etc.

Multi-drug stamens: filaments are separated and anthers are United, such as sunflower and impatiens.

4. Pistil

Pistil is located in the center of the flower, which is another important part of the flower. It consists of stigma, style and ovary. Different kinds of plants usually have different types of pistils, positions of ovaries and types of placentas.

(1) pistil type

Pistil is made of abnormal leaves, which are called carpels. The edge seam of carpel is called abdominal seam, and its back (equivalent to the midvein of leaf) is called back seam. According to the number and clutch of carpels, pistils can be divided into the following types (as shown in the following two pictures).

Pistil type

A. Free pistils, each carpel is completely separated and placed on the same receptacle;

B-D. Syngynous pistil (B. Ovary syngynous, stigma and style separated; C. the ovary and style are combined into one, and the stigma is separated; D. Ovary, style and stigma are all connate)

Schematic diagram of carpel edge healing and pistil formation process

A, B and C represent the process that an open carpel gradually rolls in and the edge heals.

1. carpel; 2. The ovule is attached to carpel; 3. Lateral veins of carpels; 4. Dorsal veins of carpels; ⑤ Back suture; 6. Abdominal suture

Single pistil: a flower has only one pistil, and this pistil consists of only one carpel, which is called single pistil, such as peach and plum.

Pistil: A flower has only one pistil, which is rolled by more than two carpels. It is called pistil, also called compound pistil, such as citrus.

Free pistil: There are several independent pistils in a flower, which are called free pistils, such as magnolia and buttercup.

(2) the position of the ovary

According to the position of the ovary on the receptacle and the joint degree of the receptacle, the ovary can be divided into the following types:

Ovary superior: The ovary is only connected with the receptacle at the bottom, which is called ovary superior. The upper position of the ovary is divided into two situations: if the ovary is only connected with the receptacle at the bottom, and the perianth and stamens are inserted into the lower ovary, it is called the lower position of the ovary, such as magnolia and wisteria. If the ovary is only connected to the bottom of the cup-shaped receptacle, the perianth and stamens are attached to the edge of the cup-shaped receptacle, which is called the periphyton of the ovary, such as peaches and plums.

Semi-inferior ovary: also called intermediate ovary. The lower part of the ovary is trapped in the receptacle and healed with the receptacle, while the upper part of the ovary is still exposed, and the rest of the flowers are planted at the edge of the receptacle, so it is also called stele sheath flowers, such as elderberry and honeysuckle.

Ovarian position

A. the ovary is superior (inferior flower); B.c. intermediate ovary

Or semi-inferior (periplexus); Lower ovary (upper flower)

Inferior ovary: the ovary is buried in the sunken receptacle and healed with the receptacle, which is called inferior ovary. The rest of the flowers are planted on the edge of the receptacle above the ovary, so they are also called excellent flowers, such as daffodils, Lycoris radiata, apples and pears. The position of the ovary is shown in the figure below.

(3) Type of placenta

Ovules are usually attached to the ovary along the ventral seam of carpels, and the attached part is called placenta. The type of placenta is shown in the figure below.

Several different ovaries and placentas

A. single pistil, single cell, marginal placenta; Free pistil, monogamy, marginal placenta;

C gynoecium, single-chamber compound ovary, placentation of lateral membrane; Syngynous pistil, multilocular compound ovary, axial placentation;

F. a gynoecium, an ovary and a central placenta.

Marginal placenta: single pistil, one ovary, ovule with abdominal seam, such as bean.

Lateral placentation: gynoecium is united, ovary has one or false chambers, and ovule is attached to ventral seam of carpel, such as wax gourd.

Placenta axillaris: Gynostemma pentaphyllum, the ovary has several cells, the edge of each carpel gathers in the center to form a placentae axillaris, and the ovule is attached to the placentae axillaris, such as citrus.

Teli central placenta: gynoecium is located in one or several incomplete chambers, and the base of the subchamber has an upward short central axis, but it does not reach the top of the subchamber, and the ovule is attached to this axis, such as Dianthus.

Basic placentation and epigenetic placentation: The ovule is attached to the base or top of the ovary. The former is composed of compositae plants, and the latter is carrot.

(6) Fruits and seeds

After flowering, pollination and fertilization, the pistil undergoes a series of changes, the ovule develops into a seed, and the ovary develops and bears fruit.

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