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Botany |
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Botany
is the study of plants. Botanical terms and concepts are the
groundwork for understanding plant health, care and
classification. When answering questions, Master Gardeners
must know how various plant parts affect plant health, which
parts are used for food and which parts are used to produce
new plants. Knowing the names of plant parts and the terms
used for grouping plants links Master Gardeners to the
universal language used by gardeners and
horticulturists.
KEY CONCEPTS
I. Plant Parts
II. Plant Processes
Return to Introduction
I. PLANT PARTS - STRUCTURE AND FUNCTION
Roots absorb NUTRIENTS and water, anchor the plant in the soil, provide support for the stem, and store food. They are usually below ground and lack nodes, shoots and leaves.
There are two major types of root systems in plants. Taproot systems have a stout main root with a limited number of side-branching roots. Examples of taproot system plants are nut trees, carrots, radishes, parsnips and dandelions. Taproots make TRANSPLANTING difficult. The second type of rootsystem, fibrous, has many branched roots. Examples of fibrous root plants are most grasses, marigolds and beans.
Since roots take in nutrients and water for a plant, it is important to promote good root development. Just because roots cannot be seen does not mean they should be neglected. The roots of ESTABLISHED plants may extend far beyond the spread of branches or foliage. If planted in rows, the roots of cultivated crops usually overlap.
The greatest number of plant roots are in the top foot of soil, with major feeder roots occurring in the top 6 inches. This knowledge is important for IRRIGATION, FERTILIZATION and CULTIVATION. The amount and location of roots may be influenced by soil characteristics.
Root hairs are small hair-like extensions of the outer layer of root CELLS. Their function is to absorb nutrients and water. Roots can have an amazingly large number of root hairs. Root hairs increase the surface area of the roots, increasing the capacity to absorb nutrients and water. For example, a rye plant can have more than 14 billion root hairs that make up a surface area about as large as a football field. Root hairs are often destroyed when a plant is dug from the soil. Careful transplanting reduces root hair damage.
The stem is the main trunk of a plant. Buds and shoots develop on stems. Stems provide structure and support for leaves, flowers and fruits. They also carry nutrients and water. In some cases, stems also store food.
Stems are generally upright and above ground, easy to locate and identify. However, there are many stems that grow below ground or are ground hugging. These stem modifications include corms, bulbs, rhizomes, runners, stolons, tubers and crowns.
A modified stem is recognizable because it includes buds and sometimes leaves.
Nodes are places on the stem where buds form. Internodes are the segments of the stem between nodes.
The quality and amount of available light and temperature affect the length of the internode. The distance between nodes can be long or short. This distance reflects growing conditions. Seedlings grown under poor light conditions may be spindly, with very long, thin and weak internodes.
One of the major functions of the stem is to move water, nutrients and food through the plant. The internal tubes in stems act like the plumbing in a house or the blood vessels in people. As in humans, this system is called the vascular system. The food-moving part of the system is called the phloem (FLOW-em) and the water-and-mineral-moving system is called the xylem (ZEYE-lem).
Another important part of the stem is called the CAMBIUM (CAM-bee-um). It is found in two separate areas. Cambium in buds produces tissue that increases the length of the stem. The cambium encircling the stem produces increased diameter or girth. Injury to the cambium layer in certain plants can kill the entire plant. For example, trees can be killed by GIRDLING damage to the cambium layer located just inside the bark.
There are many stem variations in plants. Some variations are forms of food, such as potatoes and asparagus. Others are forms sold in dormant condition for introduction into the landscape as new plants, such as dahlia tubers and tulip bulbs. The runners of strawberries are an example of a stem modification (stolon) used for PROPAGATION. Rhizomes (RYE-zohms), the horizontal underground stems of plants, such as bentgrass, allow the spreading of plants.
Leaves are lateral outgrowths from the stem. The main function of leaves is food production for the plant. Leaves have evolved into many shapes and sizes, reflecting adaptations to the environment. Leaves are most commonly flat, broad and green. This maximizes their function of absorbing sunlight and transforming it into food.Leaves have a protective layer on the outer surface of their cells called the cuticle (Q-tick-uhl). This protective layer reduces the exchange of water and gases and prevents some disease-causing organisms from entering. The cuticle is made up of a waxy substance called cutin (Q-tin). The cuticle helps prevent DEHYDRATION.
New seedlings and houseplants should be gradually moved into sunlight. This allows the layer of cutin to build up gradually and protect tender plants from SUNSCALD. Sunscald is the result of too much water being lost from heat and wind. This waxy layer in some instances makes it difficult for herbicides to stick to and enter the leaf.
For leaves to release and take in gases (carbon dioxide, oxygen) and water vapor, the leaf surface has tiny openings called STOMATA (stow-MAH-tah). The plant can regulate the size of
stomata by water pressure in the GUARD CELLS that surround the stomata. When the guard cells fill with fluid (become turgid), the stomata open allowing moisture to escape. The stomata close as the guard cells lose fluid (become flaccid), conserving moisture within the leaf.
The first leaves to appear when the seed germinates are called seed leaves or cotyledons (cot-uh-LEE-dens). These serve as stored food for the seed.
Leaves can be modified into several forms, such as SPINES, which function to protect the plant; TENDRILS, which support the stem; and brightly colored BRACTS, which may be mistaken for flower petals. Leaves function in food storage and can act as protection, as in bulbs.
Buds are undeveloped shoots and flowers. Buds are classified terminal or lateral. Another term for terminal is apical. Terminal buds can be identified by their location at the tip of a stem. Lateral buds are located at the sides of the stem.
Flower buds are normally larger than VEGETATIVE buds. Cabbage and head lettuce are examples of very large terminal buds. Brussels sprouts are edible lateral buds. Broccoli is an example of edible flower buds.
A remaining type of bud, ADVENTI-TIOUS (ad-ven-TISH-us), forms at any other location. Adventitious buds may form on the internode of the stem, at the edge of a leaf or at the cut on a stem or root. Stem and leaf cuttings develop roots from adventitious buds.
Flowers are the seed-producing parts of a plant. The function of flowers is sexual reproduction.
The pistil (PISS-till) is the female portion of the flower. It includes the stigma, the surface that captures and holds pollen, and the style, the connection between the stigma and the OVARIES.
The stamen (STAY-men) is the male portion of the flower. It includes the filament which holds the anther (ANN-thur). The anther is where pollen is formed and held until released.
A flower that has both male and female parts is called a complete or perfect flower. Flowers that have only male or only female parts are called incomplete or imperfect.
Plants with incomplete flowers are divided into two groups. The monoecious (moan-E-shuss) plant group has male and female flowers on the same plant. Monoecious means "one house." Examples of monoecious are corn and squash. The tassel at the top of corn contains the male flower, and the ears hold the female flower. Squashes bear only male flowers early in their life cycle, but later in the growing season produce both male and female flowers.
Plants that have only male or only female flowers on a single plant are called dioecious (die-E-shuss). Dioecious means "two houses." Hollies are an example of dioecious plants, since each holly plant has either male or female flowers. A plant of each sex must be planted in close proximity to produce berries on the female plant.
Other external parts of flowers include SEPALS (SEA-pulls) that are usually green and enclose the other parts of the flower in the bud. Petals are usually brightly colored and may contain aromatic substances as well as nectar glands.
Fruit is a ripened ovary or group of ovaries containing the seeds. It may include adjacent tissue that fuses with the ovary. Once the ovary is fertilized, the seeds develop and the ovary enlarges forming the mature fruit.
A simple fruit forms from the ripening of the ovary of a single pistil. Examples of simple fruits include peanuts, sunflower seeds, grain (corn, barley, rice), acorns, walnuts, tomatoes, grapes, eggplants, citrus fruits, and apples.
Aggregate fruit form from flowers with several simple pistils, such as raspberries and strawberries.
Multiple fruit forms from a cluster of several flowers. A fruit is produced by each flower and these fruits merge into a multiple fruit. Pineapple, mulberry and Osage orange are examples of a multiple fruit.
The terms fruit and vegetable are somewhat confusing because they have both a botanical and a common usage. Botanically, a fruit always develops from a flower and is composed of at least one ripened ovary. Botanically, a vegetable is any edible part of a plant other than the flower.
In popular usage a fruit is an edible plant part that is sweet and eaten as a dessert. The popular use of the term vegetable is a plant part that is edible, but not particularly sweet.
Many fruits, such as tomatoes, squash, cucumbers, corn and eggplant, are popularly called vegetables. However, only one vegetable, rhubarb (the edible petiole), is used as a fruit.
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