There is a certain relationship between the locations of corn roots, stems, leaves, ears and other organs. The morphological characteristics, growth characteristics and relationships between each organ have their own characteristics. And certain characteristics and certain rules, understanding these is very important for corn cultivation.

(1) Roots

The root system of corn is a fibrous root system, consisting of embryos and nodes.

1. Radicle

The radicle is formed when the seed embryo develops. There is only one radicle. When the seed germinates, it first breaks through the radicle sheath and extends out. After the radicle extends out, it grows rapidly and extends vertically deep into the soil, up to 20-40 cm long.

2. Nodal roots

Insert at the base of the internodal meristem of the stem. The nodal roots that grow from underground stem nodes are called underground nodal roots, and the nodal roots that grow from above-ground stem nodes are called above-ground nodal roots, which are also called rooted roots, supporting roots, etc. Nodal roots are botanically called adventitious roots.

3. Root structure and function

The structure of corn root includes epidermis, cortex and stele. Its physiological function is mainly to absorb water and inorganic nutrients from the soil with root hairs and root tip epidermal cells. The water and inorganic nutrients reach the xylem vessels through the cortex, and then are transported to the stems, leaves, ears, and grains. At the same time, the organic matter synthesized by the above-ground green tissues reaches the roots through the sieve tubes for root growth. Therefore, the mesocolumn tissue is a transportation pipeline for water and organic and inorganic nutrients. also. Corn roots also have the function of converting sugar into organic acids, producing polyamino acids and synthesizing proteins.

The radicle and nodal roots have different effects on the growth, development and productivity of the plant due to their different development time, root size, and functional strength. The root pruning test proves that the higher the layer node position, the greater the effect on plant growth and yield. When aerial roots are inserted into the soil, the order of the functions of each root layer is aboveground nodal roots, aerial roots, underground nodal roots, and radicle roots. The same type of root has a higher root position and a greater effect. Aerial roots are also the main root system that prevents corn lodging.

(2) Stem

1. Morphological characteristics of the stem

There are many nodes on the corn stalk, each node grows a leaf, and the number of stem nodes is corresponding The variation is in the range of 8-40. The number of stem nodes located underground is generally 3-7, and more can reach 8-9, while the number of stems above ground is 6-30 or more. Generally speaking, late-maturing tall stalk types have many stem nodes, while early-maturing short stalk types have fewer stem nodes.

The height of corn stalks varies greatly depending on the variety, soil, climate and cultivation conditions. For the dwarf type, the plant height is only 50-80 cm; for the tall type, the plant height can reach 300-400 cm; and for the giant type, the plant height can be as high as 700-900 cm. Generally speaking, short stalks have a short growth period and low yield per plant; tall stalks have a long growth period and high yield per plant. When the soil, climate and cultivation conditions are suitable, the stems will grow taller and the yield per plant will be higher.

2. The structure and physiological function of the stem

The anatomical structure of the corn stem, the outermost layer is called the epidermis, and within the epidermis is the mechanical tissue, including several layers of siliceous thick-walled cells. ; The epidermis and mechanical tissue have the function of protecting and reinforcing the stem, and distribute the leaves and ears in a certain pattern to fully carry out photosynthesis. The mechanical tissue is lined with loose parenchyma cells, called basic tissue. It is like a warehouse and has the function of temporarily storing nutrients.

Except for the top 4-6 nodes of the corn stem, axillary buds can be formed in the remaining leaf axils. Usually only the upper 1-2 axillary buds can develop into ears. The axillary buds at nodes 1-7 at the base of the stem can form side branches, called tillers; the axillary buds in the middle of the stem stop developing when they differentiate to a certain stage, showing a shrunken state. They generally cannot form fruit ears because they consume nutrients and should be removed as soon as possible. However, for sweet and popcorn corn, tillers can often develop poplar ears.

(3) Leaves

1. Morphological characteristics of leaves

Corn leaves are arranged alternately on the nodes of the stem. The whole leaf can be divided into three parts: sheath, blade and ligule.

The leaf sheath tightly wraps the internodes. Its length is longer than the internodes in the lower part of the plant, and shorter than the internodes in the upper part. The leaf sheaths are thick and hard. The leaves are attached to the leaf ring at the top of the leaf sheath. A main vein runs through the center of the leaf. There are many lateral veins running parallel to both sides of the main vein. The edges of the leaves often have wavy wrinkles. Most corn leaves have hairs on the underside, and only the first to fifth leaves at the base are smooth and hairless. This feature can be used as a reference for judging the position of corn leaves. The corn leaf ligule is located at the junction of the leaf sheath and the blade, and is a colorless film close to the stalk.

2. Leaf structure and function Leaf is composed of epidermis, mesophyll and vascular bundle.

Leaves are composed of epidermis, mesophyll and vascular bundles. The epidermis is divided into upper and lower epidermis. There are many small dumbbell-shaped holes on it, called stomata, which can automatically open and close to exchange gas with the outside world. There are special large cells on the upper epidermis of leaves, called motor cells, with large vacuoles inside them, which play a regulatory role when the weather is dry or the water supply is insufficient. The mesophyll is located between the upper and lower epidermis. There are many chloroplasts in its cells, which contain chlorophyll. It is the main organ for manufacturing organic substances. The veins in the leaves are vascular bundles, which are conduits for transporting water and nutrients within the leaves. The leaf sheaths are tough and tightly wrap around the internodes, thus strengthening the stem.

The main functions of leaves are photosynthesis, transpiration and absorption.

(4) Inflorescence

Corn is a monoecious and cross-pollinated crop that relies on wind pollination. The natural hybridization rate is generally around 95, making it a cross-pollinated crop.

1. The male inflorescence, also called the tassel, is located at the top of the stem. The main axis of the tassel is connected to the stem and branches out into several branches. There are two rows of paired spikelets on the branches. Each spikelet includes two guard glumes and two male flowers. Each male flower consists of inner and outer lemma. , lodicules and three stamens. The stamens have long filaments at the top of the anthers, and the anthers produce pollen. After the male spikelet matures, the blades expand, the guard glomes open, the filaments elongate, and the anthers are exposed outside the globus. They slowly disperse the powder in the breeze, which is called flowering. Generally, it takes 3-5 days for the tassel to extend from the top leaf. flowering. The flowering sequence starts with the main axis and then the branches. The main axis and branches bloom first with spikelets in the middle and upper parts, and then open upwards and downwards. It takes 7-10 days for a tassel to bloom and end. The peak period is from the third to the fifth day after flowering. The male flowers of corn bloom day and night. When the weather is sunny, the flowering is most in the morning and decreases significantly in the afternoon. In rainy weather, the flowering time is delayed.

2. Characteristics and functions of the female inflorescence

The female inflorescence of corn is also called the female ear, which develops into an ear after fertilization. The fruit ear is attached to the top of the ear stalk. The ear stalk is a shortened stem with multiple dense nodes and internodes. Each node bears a bract formed by a sheath. The ear bracts generally have 6-10 pieces. Their texture is tough and tightly wraps the female ear. It has the function of protecting the fruit ears, reducing the invasion of diseases, insect pests, wind and sand and the loss of water in the ears. The length of the bract leaves varies among varieties. If the bract leaves are too short, it will affect the development of the top kernels and easily cause baldness and damage by diseases and insect pests.

Many sessile female spikelets grow in pairs around the female ear. Each spikelet has two short and wide glumes and two florets. Among them, one degenerates and loses the ability to fertilize. The infertile floret, the other one develops normally and has the ability of fertilization and fruiting, so it is a fertile floret. The female floret includes inner and outer lemma and pistil; the pistil is composed of ovary, style and stigma. The style is slender, the stigma is bifurcated and covered with The hairs secrete mucus and adhere to pollen. There are spikelets of flowers arranged in pairs on the ear. Since one flower is degenerated and the other is strong, the number of kernels in the ear is an even number, usually 14-20 rows, as few as 8-12 rows, and as many as 24 rows. The number of rows is important. High-yielding traits, generally medium-sized ears can bear about 400-500 grains, and under high-yield conditions, 600-800 grains can be produced.

After the female bracts extend from the leaf axils, they are called heading. After the filaments expose the bract leaves, it is called silking, and the ear can also bloom. Generally, the flowering period of female ears is 3-5 days later than that of male ears, and the number of days between them varies depending on the variety and fertilizer and water management. During the jointing and booting periods, fertilizer and water management are appropriate, and the interval between male and female flowering periods is shorter; soil drought will lengthen the interval, resulting in missed flowering periods, poor pollination and fertilization, and resulting in grain baldness.

The filaments in different parts of the female ear are drawn out at different times. Generally, the middle and lower 1/3 of the ear are the earliest, followed by the base, and the top is the latest. The filaments of the female ear are generally 20-30 cm long. If pollination is delayed, the filaments can be extended to about 50 cm.

3. Pollination and fertilization

The pollen mother cells in the anthers undergo secondary division to form pollen. The pollen mother cell divides for the first time to produce a cell wall and forms a dyad; after the second division, it produces a transverse wall and becomes a tetrad, which then develops into four grains of pollen. Mature pollen grains are round in shape, smooth in surface, light yellow in color, and have a germination hole. The vitality of corn pollen can be preserved for 5-6 hours under suitable conditions of temperature and humidity in the field. After 8 hours, the vitality decreases significantly, and after a day and night, the vitality can be completely lost. Therefore, when performing artificial assisted pollination, it is necessary to pollinate while collecting pollen.

There is an ovule in the ovary of the pistil, and its center is called the nucellus, which contains the embryo sac and contains reproductive cells. The nucellus is surrounded by one and two layers of cells (integument). There is a small hole at one end of the integument, the micropyle, through which the pollen tube enters the nucellus. After the pollen tube enters the nucellus, two sperm are released. One sperm combines with the egg cell to form a zygote, which will develop into an embryo of the seed. At the same time, the other sperm combines with one of the two polar nuclei and then with the other polar nucleus. Fusion into an "endosperm nucleus" will develop into endosperm.

The filaments have a long lifespan and can last for 10-13 days after spinning. During this period, any part of the filaments can accept pollen. However, the pollination ability is strongest 2-3 days after all the filaments are drawn. After that, the viability of the filaments gradually decreased.

(5) Seeds

1. The structure and composition of seeds

The seeds of corn are fruits, which are called seeds or grains in production. Its shapes include dent type, nearly round type, and hard grain type. The grain color is mostly yellow or white, but also purple, red and mottled.

Corn seeds are composed of seed coat, endosperm and embryo.

Seed coat: It is composed of the pericarp developed from the ovary wall and the seed coat developed from the inner integument. The pericarp and seed coat are collectively called the seed coat. The seed coat is mainly composed of cellulose. It has a smooth surface and is generally colorless. It has the function of protecting the contents and accounts for about 6-8 of the total weight of the seed. Endosperm: located within the seed coat and accounting for the total weight of the seed. 80-85. There are two types of endosperm. One is powdery endosperm, which has a loose structure, is opaque, contains more starch and less protein. The other type is horny endosperm. The starch granules contain mostly protein and colloidal carbohydrates, making it tightly organized and translucent. The structure of the endosperm and the content and distribution of protein are one of the basis for corn classification. For example, hard corn seeds have horny endosperm distributed on the four sides and floury endosperm in the center. Dent corn seeds have horny endosperm distributed on both sides. , the top and center are distributed with floury endosperm.

Embryo: Located at the base of one side of the seed, accounting for 10-15 of the total mass of the seed. The embryo is actually a corn plant that is still growing, consisting of embryo, hypocotyl, radicle, and cotyledon (scutellum). The upper end of the embryo is the germ. The outside of the embryo is the coleoptile, and the coleoptile is surrounded by several ordinary leaf primordia and the tops of stems and leaves that slowly develop into stems and leaves. The lower end of the embryo is the radicle. The radicle is surrounded by the radicle sheath. The radicle sheath is in the young embryo and connects the embryonic stem. The embryo and radicle are connected by a homocotyl. The hypocotyl is tightly wrapped around the endosperm and has a scutellum for absorbing nutrients from the endosperm during seed germination.

Corn kernels are starchy seeds, with carbohydrates accounting for about 73% of the dry matter of the kernels, protein and fat accounting for 9-11 and 4-5 respectively, and water accounting for about 12%. Corn protein contains gliadin 4.21, Wheat protein 3.25, corn protein 1.99. The granular ones inside the seeds are called aleurone grains. The fat of corn is a semi-dry vegetable oil composed of approximately 72.3% liquid fatty acid and 7.1% solid fatty acid. In addition, there are a small amount of crude fiber and elements such as phosphorus, sulfur, calcium, and ash in the seeds.

The distribution of various components in seeds is: starch accounts for about 98% in the endosperm, about 1.5% in the embryo, and only about 0.5% in the cortex; protein accounts for 7.5% in the endosperm, 22% in the embryo, and 3% in the cortex; about 83.5% fat is stored In the embryo, about 15% is in the endosperm, and about 1.5% is in the cortex. The energy content of corn kernels is 365 kcal per 100 grams, which is higher than that of rice and sorghum.

Corn kernels are the largest among cereal crops. The thousand-kernel weight is generally 200-350 grams, the smallest is about 50 grams, and the largest reaches 500 grams. The kernel test weight per liter is about 650-750 grams. The kernel yield is, that is, Grains account for a percentage of the weight of the ear, generally about 75-85

2. Seed formation process

After fertilization of the ear, the filaments wither, that is, they transition into a process centered on grain formation. period. The seed formation process is roughly divided into four stages: seed formation stage, milk ripening stage, wax ripening stage and complete ripening stage. The number of days required for each period varies depending on the species and environmental conditions. Taking summer corn as an example, the process is:

Kernel formation period: About 15 days after silking, the ear and kernels increase in size, the kernels become capsule-shaped, and the endosperm becomes clear water. When the embryo enters the differentiation and formation stage, the grains have a lot of water and little dry matter accumulation. Ten days after silking, the ear length has reached normal size, the thickness has reached 88% of the mature stage, and the embryo and endosperm can be separated. The grain moisture varies between 90-70, which is in the moisture growth stage.

Milk ripening period: It lasts for 20 days from half a month after silking to around 35 days. The milk gradually becomes milky and then paste-like. At the end of this period, the fruit ears become thicker. The weight, grain, embryo and volume are all the largest. The weight of the grains increases rapidly, reaching about 60-70% at the maturity stage. This is an important stage of grain formation. The moisture content of the grains varies between 70-40%. About half a month after pollination, the embryo has the ability to germinate. The germination rate of seeds at the end of milk-ripening stage 35 days after pollination can reach 95%, and the yield per acre is also high, indicating that harvesting corn seeds early when necessary will not affect germination.

Wax ripening period: about 35-50 days after silking, lasting 10-15 days. During this period, the kernels are in the shrinkage stage, the kernel moisture is reduced from 40% to 20%, and the ear diameter and kernel volume are slightly reduced. Small, the endosperm changes from mushy to waxy. The accumulation of dry matter in the grains continues to increase, while the speed slows down, but there is no obvious termination period.

Full ripening stage: The seeds become hard, difficult to be scratched by nails, have luster, and show variety characteristics.