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Plant Anatomy |
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Plant Anatomy |
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Leaves
Leaves come in a wonderful array of sizes, shapes, textures, and colors, but whatever the form, they all serve a common function. Leaves manufacture the sugars and other compounds that serve as food for plants. To perform this manufacturing process, called photosynthesis, leaves need several ingredients: light, chlorophyll, carbon dioxide, and water.
To intercept as much light as possible, most leaves are flat and face broadside to the sun. Also, they are positioned to avoid shading other leaves on the same plant. When light strikes a leaf, much is reflected, however some is absorbed by the chlorophyll in the leaf tissue.
Leaves absorb carbon dioxide through tiny pores called stomata. These pores are usually on the underside of the leaf, where the chance of clogging is reduced. Monocots, like turf, corn and daffodils have stomata on both sides of the leaf. Stomata also act as cooling mechanisms. As much as 98% of water intake from the roots can be lost to transpiration which cools the leaf surface during period of high heat. If the plant starts to wilt the stomata will automatically close to conserve water.
The plant uses the energy from the sun to split water molecules into their component parts: hydrogen and oxygen. The plant discards the oxygen and mixes the hydrogen with carbon dioxide from the air to produce glucose and other sugars for food. The glucose is only the building block for other compounds in the plant. Starch, fibrous cellulose, proteins, oils, vitamins, pigments are all made from the sugars produced by photosynthesis.
Types of leaves:
 Needle-like |
Opposite |
Pinnately-Compound |
Scale-like |
Palmate |
Trifoliate |
Whorled |
Strap-like (monocot) |
To become an accomplished gardener you need to know that the health and yield of the above ground parts of their plants depend on vigorous roots to supply water and nutrients, provide support, and anchor the plants in the soil.
The first root that develops from a seed is the taproot or primary root. It will grow straight down and may grow for several inches before any aboveground growth is seen. In some cases the taproot remains dominate for the life of the plant, such as carrots, dandelions, and spinach. However, most plants have roots that radiate out in many directions splitting and rebranching many times.
Root Function
The most important function of roots is collecting water and nutrients from the soil. This job is the task of the youngest, most tender parts of the root system - the growing root tips and root hairs. As roots grow, these tips and hairs are continually exploring new soil looking for nutrients. Water and nutrients are transported up through the plant in the xylem, a hollow chain of cells just under the stem surface. In the opposite direction, the roots receive sugars from the leaves through the phloem.
The roots of many kinds of plants grow in symbiosis with one or another kind of fungus. The fungus absorbs dissolved minerals, particularly phosphorous, from the soil and passes them into the plant roots in return for sugars and other organic compounds. These mycorrhizal associations benefit both the plant and fungi.
Some plants, particularly members of the legume family such as beans and clover, host bacteria in their roots. Infected roots have characteristic round swellings called nodules. Even though the bacteria consume a share of the plant's sugars, the plant benefits because these bacteria can gather nitrogen from the air and convert it into compounds that roots can absorb.
Types of roots:
Stems are the support structures of a plant. They can be classified into two general categories: woody and herbaceous. Herbaceous stems may stand erect on their own as in aster and purple coneflower or they may lie prostrate on the ground like cucumbers and pumpkin, or they may spiral around a support while growing upward as in clematis. Most herbaceous stems can not live more than one growing season, although the root system will. trees and shrubs are said to have woody stems. A tree is a relatively large woody plant ordinarily with a single upright stem, the trunk. A shrub, by contrast, usually has several main stems and branches more profusely than a tree. One other type of stem is called Liana which grows in temperate climates. Grapes, poison ivy, and Virginia creeper are examples of Liana. The climbing action of these plants is aided by modified branches called tendrils that latch onto any surface and provide support. Another example of modified branches are the sharp thorns of Hawthorn and Honey Locust. Yet another example of modified branching are Haustoria which penetrate the tissue of a host plant and absorb nourishment in a parasitic habit. Stems that are short, erect, food-filled and usually located below the soil surface are the Corms of crocus and gladiolus. Stems which begin erect but curve over, touching the ground at the tip, are called stolons. They are characteristic of briar roses and raspberries. Both stolons and runners are considered reproductive structures. Horizontal stems growing below the surface of the ground are rhizomes. They are common in ferns, lilies, irises and goldenrod. Often they contain large amounts of food. Tubers are the underground stems of potatoes.
Back to Botany 101 or to The Institute.
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