Plant Connections Leader's Guide—Lesson 4: How to Grow Plants1
Plants exist in close association with each other and their environment. Each part of a natural or artificial environment effects the survival and quality of plants. Environmental factors such as sunlight, water, air, nutrients, and a proper temperature help to regulate plant growth. When one or more of these factors are missing, the plant will not grow as it should and may die.
Plant propagation refers to the sexual and asexual reproduction of plants. Sexual propagation in plants is the reproduction of plants by seeds. Since most plants reproduce naturally from seeds, this method is often the easiest and least expensive. Sexual reproduction takes place in the flower of the plant. A typical or complete flower consists of four parts:
Sepals—leaf-like structures beneath the petals which form a protective covering around the flower until it opens. The calyx is made up of all the sepals on one flower.
Petals—brightly colored leaf-like part of a flower which attracts pollinators.
Stamen—the male reproductive portion of a flower. A stamen consists of a filament or stalk which supports the anther. The anther produces the pollen or male sex cells.
Pistil—the female reproductive portion of a flower. A pistil consists of the stigma, style, and ovary.
Examples of complete flowers include apple, lily, and pea. Flowers that lack sepals, petals, stamens, or pistils are known as incomplete flowers.
Flowers are further grouped by the presence or absence of stamens and pistils. Perfect flowers contain both stamen (male) and pistil (female) reproductive structures in the same flower, while imperfect flowers contain only the stamen or pistil. Examples of imperfect flowers include corn, holly, squash, and willow.
Pollination occurs when a pollinator, such as wind, insects, or animals, transfer pollen grains from the anther to the stigma. The pollen grows from the stigma down the style to the ovary. Fertilization occurs when the male and female cells unite to produce a seed. After pollination and fertilization, the flower petals begin to drop and the ovary enlarges and develops into a fruit. The fruit is the seed bearing organ of the plant. There are basically two types of fruit:
Fleshy fruit—The mature fleshy fruit is composed of a soft fleshy material with seed or seeds inside. Blueberry, peach, tomato, and melons are all fleshy fruits.
Dry fruit—The dry fruit consists of seeds enclosed in a fruit wall that is hard and brittle when mature. Pea, sunflower, and oak produce dry fruits.
Seeds are the mature, fertilized ovules or eggs. They consist of a seed coat, endosperm (food storage tissue), and embryo. Seed germination is a process that begins when the seed absorbs water (imbibation). Besides water, seeds also need oxygen, warmth, and some need light to germinate. The germination process is complete when the seedling can manufacture its own food.
Asexual propagation is the production of new plants from stems, leaves, or roots of a parent plant. In this method of plant reproduction no seeds are used, just portions of the parent plant which are placed in soil, soil-less media (potting soil, vermiculite, peat moss), or even test tubes containing nutrient rich agar. Asexual propagation permits growers to produce more plants faster, especially in cases where seeds are difficult to germinate or are not viable (alive). One of the most important benefits of asexual propagation is that the plants produced are genetically identical to the parent plant.
The most common method of asexual propagation is the use of cuttings. Cuttings are detached portions of the plant, such as stems, leaves, or roots which grow into complete plants. Cuttings are often treated with a root inducing hormone and placed in an environment that favors root initiation and development. Other methods of asexual propagation include layering, division, and grafting.
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