The fruit is formed from the ovary of the pistil after fertilization and is the most characteristic organ of a flowering plant. If the fruit is formed only by the pistil, it is called true. If other parts of the flower (receptacle, integument) also take part in the formation of the fruit, it is called false.
Fetal functions- protection of the delicate tissues of the developing seed from the effects of various unfavorable conditions:
- drying;
- mechanical damage;
- low temperatures;
- favor the spread of seeds.
It is because of the presence of fruit that flowering plants are called angiosperms.
Structure of the fetus: when the fruit is formed, the walls of the ovary grow and form a pericarp, consisting of three layers: outer, middle and inner. In different plants, the ratio of the thickness and density of all three layers is different and is a species characteristic.
The outer layer is usually thin, but the middle layer can be thick, juicy and meaty with a lot of sugar (cherry, apricot) or oil (olive). The inner layer is also thin, but can change and turn into stony tissue - a stone (peach, plum). Unripe fruits are green in color because they contain a lot of chlorophyll.
Fruit classification
Dry and juicy fruits vary in water and nutrient content. The retained outer skin of the ovary on the surface of the dry fruit forms various outgrowths and appendages in the form of spines, hairs, attachments, and winglets. Juicy fruits have an expanded, fleshy middle layer of pericarp and contain one or more seeds.
Fruits can be simple or complex. Simple ones contain one or many seeds. Simple single-seeded juicy fruits are represented by drupes (cherry, apricot). The inner layer of such a fruit consists of stony cells that form a “stone” with the seed. Multi-seeded fruits are berries (grapes, currants, tomatoes), with several seeds embedded in their juicy pulp.
Complex, juicy fruits are formed either from several individual flowers, like the infructescence of a mulberry, or from several pistils of one flower, like the polydrupe of a raspberry. In addition, their difference is that the infructescence falls off entirely after ripening; the multidrupe can crumble into individual fruits.
Dry fruits do not have juicy pulp and contain one, several or many seeds. Dry, indehiscent fruits are usually single-seeded. This is a nut (hazel) with a hard, woody fruit. The achene (sunflower) has a leathery fruit. The walls of the grain (rye) grow tightly together with the seed coat.
Dry dehiscent fruits contain several or many seeds, their walls may be woody, leathery or membranous:
- Leaflet- single-locular leathery fruit, opening along the seam of a fused carpel (delphinium, peony);
- bean- a single-locular fruit opens from the top to the base with two valves, on the walls of which there are seeds (beans, peas);
- pod- a two-locular fruit with seeds located on a membranous septum (cabbage, radish). The pod opens like a bean with two flaps, but from the base to the apex. If the length of the pod is small and exceeds the width only by one and a half to two times, it is called a pod (shepherd's purse);
- box- the fruit is in the form of a box, opens with a lid (henbane), holes (poppy), cloves (cloves).
In addition to the listed types of fruits found in the most common plants, there are others.
The described classification of fruits is artificial, since it mainly takes into account only their morphological characteristics. Attempts are being made to create a natural, evolutionary classification of fruits.
Distribution of fruits and seeds
In flowering plants, seeds, as a rule, after ripening lose contact with the mother plant and germinate somewhere else. Distribution of fruits and seeds is carried out by wind, water, animals, humans, or seeds are scattered when the fruits open.
So, by the wind seeds or fruits of plants equipped with hairy tufts (dandelion, sow thistle) and wing-like appendages (birch, maple) are dispersed. In steppe plants called “tumbleweeds,” the wind carries a spherical plant broken off at the root collar, dispersing seeds over long distances (steppe tumbleweed).
Plants whose seeds can float disperse water(white water lily, coconut palm).
Fruits and seeds, edible or equipped with various attachment devices, are distributed animals and humans. They cling to animal fur, human clothing (burdock, string), and stick to the paws and beaks of birds. Juicy fruits are eaten by animals (strawberries, raspberries), their seeds are not digested and fall into the soil along with excrement. Many animals (squirrels, hamsters) store seeds (acorns, nuts) for the winter in different places, but not all of them are found, and then the seeds germinate where they were brought.
Humans play a major role in the distribution of seeds of cultivated plants, sowing them in different parts of the globe. Along with the seeds of cultivated plants, seeds of wild plants are often included. When transporting goods using hay or straw as packaging material, where a wide variety of seeds are usually found, man scattered these seeds along highways, dirt roads and railways. From these initial places, the “new settlers” spread widely to new places in their usual ways.
The meaning of flowers, fruits and seeds in nature and in human life
Flowers are the sexual reproductive organs of angiosperms. After the processes of pollination and fertilization, fruits and seeds are formed from parts of the flower. Thanks to the presence of these organs, flowering plants can reproduce and spread to new territories.
Nectar, pollen, as well as all parts of flowers, fruits and seeds of different plant species can be used as food by animals from invertebrates to humans, especially insects: for many of them flowers, fruits and seeds are not only food, but also a place for reproduction and development.
Flour for making bread is processed grains of cereals, cereals are processed fruits and seeds of rice, buckwheat, millet, barley and other plants. Valuable food products are the seeds of peas, beans, soybeans, beans, coconut palms, breadfruit, pineapple and other plants.
Edible vegetable oils are obtained from the seeds and fruits of sunflower, cotton, olives and others. Fruits and berries of various fruit and vegetable crops are of great importance in the human diet: apple trees, pears, cherries, plums, oranges, lemons, gooseberries, currants, tomatoes, cucumbers, pumpkins, watermelons and many other plants.
The fruits of pumpkins, fodder watermelons, zucchini and other plants are used to feed livestock. Raw cotton is obtained from the fruits of the cotton plant, which is divided into fiber (30-40%), used for the production of cotton fabrics, and seeds (60-70%). The seeds contain 24-26% oil, 20% protein. The oil is used for food and for the preparation of technical oils.
Thus, all cultivated plants grown in crop production produce fruits and seeds, which are used by humans in one form or another.
Some plants have flowers or inflorescences that have nutritional value (cauliflower, artichoke, lotus).
Such a branch of plant growing as decorative floriculture is of great importance. Flowers decorate our houses, streets, gardens and parks. The aesthetic significance of flowers and plants, which cultivate a sense of beauty in a person, is reflected in fiction, fine arts, and architecture.
Fruit
Lecture No. 6
Fruit. General characteristics. The structure of the fruit. Principles of fruit classification. Morphogenesis of fruits.
The fruit is the most characteristic organ of angiosperms. It is formed as a result of the changes that occur in the flower after fertilization. Sometimes the fruit is defined as a mature flower.
The diversity of fruits is determined by three groups of characteristics:
!) structure of the pericarp;
2) by the method of opening or disintegration;
3) features related to distribution
The pericarp is an overgrown and often highly modified wall of the ovary, which, together with other organs of the flower, is included in the composition of the fruit. In the pericarp there is an outer layer - the exocarp and an inner layer - the endocarp, and sometimes a middle layer - the mesocarp. All three zones can be most clearly distinguished in drupe type fruits - a thin leathery exocarp, a fleshy mesocarp and a hard endocarp. In typical berries, the entire pericarp is juicy and individual layers are difficult to distinguish. Also, in dry fruits, in some cases one can detect layers of differently differentiated cells (sunflower), while in others the pericarp is completely homogeneous (hazel).
During the process of ripening, the pericarp undergoes very significant biochemical changes. In the juicy pericarp, sugars, vitamins, various aromatic substances, and fats accumulate, which is the basis for the use of fruits by humans and chlorophyll-bearing layers. The fruits become brown or acquire a bright color due to the formation of carotenoids, anthocyanins, etc.
Principles of fruit classification
The defining morphological feature of the fetus is the type of gynoecium from which it develops. In connection with the apocarpous and cenocarpous types of gynoecium, apocarpous and cenocarpous fruits are distinguished. Among apocarpies, a distinction is made between polymeric (i.e., arising from several or many carpels) and monomeric multiseeded fruits. In the coenocarp type, one can distinguish between upper and lower multi-seeded and single-seeded variants.
In some cases, artificial classification of fruits is possible, based mainly on external morphology. The latter are divided into dehiscent and non-dehiscent.
Morphological classification of fruits
Based on the properties of the tissues of the fruit walls, dry and juicy fruits are distinguished.
Dry dehiscent fruits
Dry dehiscent fruits are usually multi-seeded. These fruits develop from one carpel (leaflet, bean) or from several (box, pod).
A leaflet is a fruit formed by one carpel and dehiscent along the suture (suturally). More often, the leaflet is not a whole fruit, but only a fruit, i.e. is part of a multi-leaflet. In some evolutionary series, the multileaf is transformed into a unifoliate. This fruit is known from some species of larkspur.
The pod develops from the superior ovary formed by one carpel. It opens along the suture from the edges of the carpel and along the midrib, i.e. in contrast to the leaflet, it opens to form two flaps. The bean is a more specialized fruit than the leaflet.
The capsule consists of several carpels and opens either with valves or holes, or forms caps.
A special type of box is a pod. It consists of two carpels with fused edges and a false septum, which develops from the placenta and divides the ovary nest into two parts. If the longitudinal dimensions of the pod are not much larger than the transverse dimensions, then it is called a pod. Pods and pods are characteristic of cabbages.
The top boxes are for henbane, tulip, flax, datura, plantain, the bottom boxes are for iris, fireweed.
A special type of fruit, a pomegranate, was formed from the lower syncarpous capsule. The pericarp is dry, opens with irregular cracks, the seed coat is fleshy.
When individual parts of the pericarp were succulentized, juicy fruits emerged from the syncarpous capsule: a berry (the upper one in a tomato, the lower one in blueberries, lingonberries, and cranberries). Apple (bottom fruit).
Fractional fruits
Fractional fruits are divided longitudinally along the partitions into lobes (mericarps), corresponding to an individual carpel.
A well-known fractional fruit is the maple bipterygoid, which develops from the superior ovary. After the fruit cracks, the lionfish do not fall off immediately, but hang on the conducting bundles for some time.
The most specialized fractional fruit is the herring (umbrella) fruit, which develops from the semi-inferior ovary. Such a fruit splits into two mericarps in the plane of fusion of the carpels.
If septa are formed in the fruit, dividing the fruit into separate chambers, completely isolated from each other, and the fruit easily breaks up into separate segments carried by wind or water, then such fruits are called segmented. The biological significance of fractional and segmented fruits is that the seed is protected by the pericarp not only during ripening, but also after separation from the mother’s body.
Dry unopened fruits
Dry fruits, unlike juicy fruits, at the time of ripening, the pericarp contains practically no water and reserve nutrients. It is inedible and serves a protective function. In many fruits, opening the dry carp allows the seeds to spread (yellow acacia, poppy). Dry, indehiscent fruits develop from an ovary in which only one seed matures, although there may be more than one ovule. The structure of the pericarp of such fruits is similar to the seed coat. The true seed coat of such fruits is obliterated (achene in Asteraceae) or fused with the pericarp (caryopsis in Poaceae). The achene (in Asteraceae) develops from the lower ovary and is the lower fruit.
The leaflet is an apocarpous, dry, single-locular, multi-seeded fruit, formed by one carpel and dehiscent along the ventral suture (on one side). Found in honeysuckle and peony.
The bean is an apocarpous, dry, single-locular, multi-seeded fruit formed by a single carpel. It opens both along the ventral suture and along the midrib of the carpel. When opened, the fruit valves twist, which is ensured by the presence and special arrangement of mechanical tissues in the mesocarp and contributes to the spread of seeds. Examples of beans: alfalfa, astragalus, clover.
The pod is a paracarpous, bilocular, multi-seeded dry fruit (in cruciferous plants). The internal septum to which the seeds are attached is not formed by the walls of the carpels, as in syncarpous fruits, but represents outgrowths of the placental grooves and is called false. It opens at two seams and is more than 4 times the width. In many plants, fruits that are less than 4 times as long as wide are called pods. Their length is either equal to the width of the fruit or greater (shepherd's purse, field lily).
Capsule is a syncarpous dry single- or multilocular multi-seeded fruit. This group usually includes dehiscent dry fruits. It is formed, as a rule, from the superior ovary, consisting of two or more carpels. They differ well in the way they are opened: by a lid (henbane, purslane), holes (poppy, bell, snapdragon), teeth at the top (some cloves, horse chestnut, cotton), longitudinal cracks from the upper to the lower end (datura, euphorbia, violets). The methods of opening the box are genetically predetermined and are systematic features. The opening mechanism is determined by the structural features of the pericarp.
Achene is a paracarpous dry single-seeded fruit formed by two carpels with a single ovule: the seed coat is highly reduced, the seed is easily separated from the peel. Typically, the achenes bear various appendages that enable dispersal (in Asteraceae).
A fractional achene is a syncarpous fruit, consisting of two achenes, which separate after ripening, but remain suspended on special legs attached to the placenta (in Umbelliferae). An achene, the pericarp of which has a leathery or membranous wing-like outgrowth, like that of an elm, is called a lionfish.
Lionfish is a syncarpous fruit, the perianth of which has a leathery or membranous wing-like outgrowth (elm, ash, birch). Maples have fractional biptera. The outgrowths ensure the distribution of fruits by the wind.
The fruit of cereals is a grain. The caryopsis is a paracarpous, indehiscent single-seeded fruit, characterized by very close contact with the seed coat, which even allows us to talk about their fusion. There are bare heads (rye, wheat, corn) and membranous heads (barley, millet, oats, rice). Films are overgrown flower scales, on which various kinds of outgrowths are often formed, facilitating the spread of fruits - feather grass. The covering layers of the grain are the pericarp and the remains of the seed coat. Underneath them is an aleurone layer with a supply of lipids and proteins. The aleurone layer is the site of the synthesis of enzymes necessary to imitate germination. The aleurone layer surrounds the starchy endosprem, which occupies up to 83% of the mass of the entire fruit, and the embryo.
Nut-like fruits are dry, indehiscent single-seeded fruits. Walnut is a syncarpous fruit, single-seeded (hornbeam, hazel). The ovary is bilocular, with one ovule in the socket. In the immature pericarp, the exocarp is sclerified, and the mesocarp is a spongy tissue that fills the entire internal space. Over time, it collapses and the space is filled with developing seed. The nut has a woody pericarp (hazel). The plume surrounding the common hazel nut is formed by bracts that retain their leafy character. The nut differs from the walnut in its smaller size (linden).
The acorn is a syncarpous fruit, a special case of a nut with a leathery, non-lignified pericarp, and has a cup-shaped plus at the base. At the first stages, the plus almost completely surrounds the ovary, and in the mature state the fruit protrudes significantly above the edge of the plus. The pistil has three stigmas, which means the fruit is formed by three carpels, two ovules are laid, but only one develops.
A nut is a dry, single-seeded syncarpous fruit (linden, buckwheat) that differs from a nut in its smaller size. Composite nut (multi-nut) – apocarpous single-seeded fruits (cinquefoil, buttercup, chastukha, gravilat). Multi-nuts include strawberry fruits, in which the receptacle grows strongly. Very close to strawberry fruits is the rose hip, in which nuts are attached inside the goblet-shaped hypanthium, and a long column protrudes out through the narrow opening of the hypanthium.
According to the morphological classification, nuts, nuts, acorns, lionfish, achenes and grains are classified as nut-shaped fruits.
Juicy fruits
Juicy fruits are those in which, by the time they ripen, a lot of water and nutrients accumulate in the pericarp tissues. The pericarp is used by animals as well as humans. The juicy pericarp promotes seed dispersal, as many fruits are eaten by animals.
Juicy fruits, like dry ones, are formed from a single-carpel or multi-carpel gynoecium. Not only the drupe, but also other parts of the fetus can become juicy: the placenta and septa in multilocular ovaries.
The citrus fruit, the hesperidium or bitter orange, develops from the superior ovary and consists of approximately 10 carpels. The partitions between the sockets of the ovary are outgrowths of the endocorpus and mesocorpus. Sacs with juice are formed in the endocorpus, completely filling the ovary sockets. Thus, the edible pulp of citrus fruits is formed by highly overgrown and juice-filled hairs of the inner epidermis of the carpels.
Pumpkin is a syncarpous juicy multi-seeded fruit, develops from the lower ovary, consists of three carpels. The boundary between carpel and extracarpel tissues is not visible. The seeds are immersed in parenchymal tissue. The exocarp is hard and woody. The pulp is an overgrown placenta (pumpkin, melon, watermelon, zucchini, banana).
Berry is an upper syncarpous multi-seeded fruit (grapes, crow's eye, potatoes, tomatoes, gooseberries, currants, blueberries, lingonberries). The mesocarp is succulent, the endocarp is absent and the seeds are in the succulent mesocarp, the seed coat is hard. A tomato berry has two carpels. The pericarp, septa and large placentas are succulent. Moreover, the placentas fill most of the ovary cavity. Placental tissues are implanted between the ovules. As it matures, this part of the placental tissue breaks down and becomes gelatinous.
Apple is a syncarpous fruit characteristic of apple, quince, and rowan trees. The apple develops from the lower ovary. Its pulp is formed by the extracarpel-leaf part of the fruit (floral tube or hypanthium). The hypanthium is an expanded receptacle with which the base of the perianth and androecium are fused. The apple is a syncarpous multileaflet overgrown with the fleshy tissue of a floral tube. At the same time, the pericarp also differentiates: the endocarp becomes hard and lines the nests of the fruit, the outer tissues of the carpel become fleshy and merge with the tissues of the floral tube.
Apple, berry, pumpkin, hesperidium are juicy multi-seeded fruits.
Drupe fruits are characterized by a clear differentiation of the carp into three zones: a thin exocarp, a thick woody endocarp (stone) and a juicy mesocarp with a large supply of nutrients (cherry, plum, cherry plum, apricot). These are apocarpous juicy fruits, mainly with one seed. In some plants (coconut, almond, walnut) the mesocarp is not succulent, but dense or fibrous (coconut palm). These are the so-called dry drupes.
A drupe is a juicy single-seeded fruit that develops from a single carpel of peripistotic flowers.
A collective drupe characteristic of raspberries, blackberries, drupes, and cloudberries. This is an apocarpous, single-seeded, juicy fruit made from small drupes located on a common receptacle. The structure of the collected drupes is typical of drupes; their number varies from 3-6 to several dozen (raspberries, blackberries). In raspberries, individual drupes form a collective fruit on a convex receptacle. Each drupe has a stony endocarp, consisting of elongated bent sclereids oriented differently in different layers. The juicy pulp is the parenchymal mesocarp. The exocarp contains epidermal hairs, which in the mature fruit hold the drupes together. After ripening, the polydrupe of raspberries is easily separated from the receptacle, while in blackberries, when harvested, it is separated along with the receptacle.
The pistil occupies the apical position in the flower. It consists of an ovary, a style and a stigma. The stigma receives pollen. With the help of a column, it occupies a position favorable for the entry of pollen. A pollen tube grows along the style, delivering male gametes to the ovary.
Ovules develop in the ovary, female gametes are formed, and fertilization occurs. The part of the ovary wall on which the ovules are formed is called the placenta. The position of the placenta in the ovary and, consequently, the position of the ovules has a regular character, constant for certain systematic units.
The pistil is a hollow organ. It is formed from the fusion of the edges of a carpel or several carpels (carpellae). There may be one or more nests in the ovary cavity.
If each individual carpel, fused with its edges, forms a pistil, the gynoecium is called apocarpous(from Greek aro - negation, karpos - fruit). There are as many pistils in a flower as there were carpels. Flowers of marigold, buttercup, raspberry and other plants have apocarpous gynoecium with many pistils. In an apocarpous pistil, naturally, there is one nest. The ovules are located on both sides of the seam, which fused the edges of the carpel. This placement of ovules is called wall-angular.
The gynoecium is called coenocarpous(from the Greek kainos, karpos - fruit), if the pistil is formed from the fusion of several carpels. Carpels grow together in different ways, so there are several types of coenocarpous pistils. A pistil is called syncarpous if each carpel, when fused, forms a closed nest. The number of nests in the ovary corresponds to the number of carpels forming the pistil. The ovules still develop at the edges of the carpels, but these edges, which bear the placenta, end up in the center of the ovary. Such a placenta is called central-angular.
If the carpels grow together only at the edges and form one common cavity of the ovary, the gynoecium is called paracarpous(from the Greek para - near), and the location of the ovules or the type of placentation is wall.
The pistil evolved from the syncarpous pistil lysicarpous(from Greek lisi - dissolution). It is assumed that during the development of the lysicarpous pistil, the walls of the multilocular syncarpous ovary are partially dissolved, and a column formed from the placenta-bearing edges of the carpels remains in the center of the ovary. Thus, in the lysicarpous ovary, the ovules, and then the seeds, are located on the central column. This type of placentation is called central (columnar).
In evolutionary terms, the apocarpous gynoecium is the most primitive. In the process of plant phylogenesis, carpels gradually grow together and their number decreases. In many plants one can see transitional forms of the pistil from apocarpous to coenocarpous, when only partial fusion of the carpels occurs at their base.
Based on their position in the plant, the ovary is distinguished between superior and inferior. The superior ovary is located at the top of the receptacle, lies freely, does not fuse with other parts of the flower. The inferior ovary is immersed in the receptacle and fuses with its walls. Sepals, petals, and stamens are located on the receptacle above the ovary. In the case of the inferior ovary, the receptacle has a concave shape.
The wall of the ovary is covered with epidermis on the outer and inner sides. The epidermis has numerous stomata, which are found on both the outer and inner sides. The cuticle is formed mainly on the outer side of the ovary.
The walls of the ovary consist of loose parenchyma tissue. The cells of this tissue are relatively small, with thin membranes and large nuclei. They are poorly specialized and retain their embryonic character, which explains the significant growth of the ovary after fertilization. Both the mesophyll and the epidermis of the ovary walls contain chloroplasts. After fertilization, the ovary grows into a fruit, and the structure of its walls changes significantly.
Stigma - specialized part of the carpel that receives pollen. The surface of the stigma is covered with conductive tissue, which often continues into the style canal. Conductive tissue is formed from the proliferation of epidermal cells and cells of the subepidermal layer. She performs a secretory role. Its cells are relatively large, thin-walled, rich in cytoplasm and nutrients. The conductive tissue creates an environment favorable for pollen germination and pollen tube development.
Column in different plants it is developed to varying degrees, in some it is absent. The tissues that make up the style are differentiated to a greater extent than the tissues that make up the ovary.
The column can be open or closed. In the open column there is a channel, the walls of which are lined with epidermis or partially with special conductive tissue, which is a continuation of the same tissue of the stigma. There is no channel in a closed column. In this case, the axial part of the column is filled with conductive fabric. Such columns are more advanced in evolutionary terms.