dormancy may be broken both naturally and artificially.
Note to the Reader:
Although the numbers of bacteria, algae, and fungi are much greater than those of flowering plants, much of this text is devoted to various aspects of flowering plants, partly because flowering plants are more abundant than other true plants and more important to humanity than all the other kinds of plants. In early editions of this book, most basic features of flowers, fruits, and seeds were discussed in a single chapter. This followed a progressive examination of members of the Plant Kingdom, beginning with the simplest forms, so that the reader could appreciate how flowering plants developed and became the most advanced and complex of all plants. Some shorter courses, however, do not cover certain reproductive and evolutionary aspects of the Plant Kingdom, and instructors differ in their assessment of the relative importance of such matters in a short course.
In recognition of this dilemma, the original single chapter is represented in this edition by Chapters 8 and 23. Chapter 8 emphasizes form and structure of flowers, fruits, and seeds, with brief reference to reproduction. Chapter 23 covers more details of the life cycle and evolution of flowering plants. Even if your course does not include Chapter 23 in the curriculum, it is recommended that you read it as an adjunct to Chapter 8.
number of years ago, an Australian farmer,
Awhile plowing a field, glanced back and was startled to see what looked like flowers being tossed to the surface of the furrows. He climbed off his tractor to take a closer look and found that what he saw were, indeed, flowers. Furthermore, the plants to which the flowers were attached were pale and had no chlorophyll. He reported his find to a university, where botanists determined that the farmer had stumbled upon the first known underground flowering plant. The plant proved to be an orchid that lived on organic matter in the soil and was pollinated by tiny flies that gained access to the below-ground flowers via mud cracks that developed in the dry season (Fig. 8.1).
The underground-flowering orchid is only one of about 240,000 known species of flowering plants. Other unknown numbers of undescribed species are established in remote areas, particularly in the tropics. The flowering plants are vital to humanity, providing countless useful products, with just 11 species—10 of them members of the Grass Family
(Poaceae)—furnishing 80% of the world's food. This subject is discussed in more detail in Chapter 24.
The flowers themselves range in size from the minute flowers of the duckweed, Wolffia columbiana, whose entire speck of a plant body is only 0.5 to 0.7 millimeter (0.02 to 0.03 inch) wide, with flowers little more than 0.1 millimeter long, to the enormous Rafflesia flowers (Fig. 8.2) of Indonesia that are up to 1 meter (3 feet 3 inches) in diameter and may weigh 9 kilograms (20 pounds) each.
Flowers may be any color or combination of colors of the rainbow, as well as black or white; they may have virtually any texture, from filmy and transparent to thick and leathery, spongy to sticky, hairy, prickly, or even dewy wet to the touch. Flowers of many trees, shrubs, and garden weeds are quite inconspicuous and lack odor (Fig. 8.3), but other flowers are strikingly beautiful, particularly when examined with a dissecting microscope. Their fragrances, which can be exhilarating to seductive or even putrid, are the basis of international perfume and pet-repellent industries.
Flowering plant habitats are as varied as their form. Besides the underground habitat mentioned in the chapter introduction, some flowering plants (epiphytes) go through their life cycles dangling from wires or other plants (Fig. 8.4). They also occur in both fresh and salt water, in the cracks and crevices of rocks, in deserts and jungles, in frigid arctic regions, and in areas where the temperatures regularly soar to 45°C (113°F) in the shade. In fact, they can be found almost anywhere they receive their basic needs of light, moisture, and a minimal supply of minerals. One species of chickweed survives at an altitude of 6,135 meters (over 20,000 feet) in the Himalaya Mountains, and fumitory plants in the same area flower even when the night temperatures plummet to -18°C (0°F).
Flowering plants can go from the germination of a seed to a mature plant producing new seeds in less than a month, or the process may take as long as 150 years. In annuals, the cycle is completed in a single season and ends with the death of the parent plant. Biennials take two growing seasons to complete the cycle; perennials, however, may take several to many growing seasons to go from a germinated seed to a plant producing new seeds, although many species that aren't annuals do produce seeds during their first growing season. Perennials may also produce flowers on new growth that dies back each winter, while other parts of the plant may persist indefinitely.
Flowering plants are currently placed in two major classes, the Magnoliopsida and Liliopsida, previously known as the Dicotyledonae and the Monocotyledonae. Despite the revised class names, the two groups are still commonly referred to as dicots and monocots. Members of the two classes are usually distinguished from one another on the basis of features listed in Table 8.1.
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