Dormancy helps keep seeds viable during unfavorable conditions. Upon a return to favorable conditions, seed germination takes place. Favorable conditions could be as diverse as moisture, light, cold, fire, or chemical treatments. After heavy rains, many new seedlings emerge. Forest fires also lead to the emergence of new seedlings.
Some seeds require vernalization cold treatment before they can germinate. This guarantees that seeds produced by plants in temperate climates will not germinate until the spring. Plants growing in hot climates may have seeds that need a heat treatment in order to germinate, to avoid germination in the hot, dry summers. In many seeds, the presence of a thick seed coat retards the ability to germinate. Scarification , which includes mechanical or chemical processes to soften the seed coat, is often employed before germination.
Depending on seed size, the time taken for a seedling to emerge may vary. Species with large seeds have enough food reserves to germinate deep below ground, and still extend their epicotyl all the way to the soil surface.
Seeds of small-seeded species usually require light as a germination cue. This ensures the seeds only germinate at or near the soil surface where the light is greatest. If they were to germinate too far underneath the surface, the developing seedling would not have enough food reserves to reach the sunlight. After fertilization, the ovary of the flower usually develops into the fruit.
Fruits are usually associated with having a sweet taste; however, not all fruits are sweet. In most cases, flowers in which fertilization has taken place will develop into fruits, and flowers in which fertilization has not taken place will not. Some fruits develop from the ovary and are known as true fruits, whereas others develop from other parts of the female gametophyte and are known as accessory fruits.
The fruit encloses the seeds and the developing embryo, thereby providing it with protection. Fruits are of many types, depending on their origin and texture. The sweet tissue of the blackberry, the red flesh of the tomato, the shell of the peanut, and the hull of corn the tough, thin part that gets stuck in your teeth when you eat popcorn are all fruits. As the fruit matures, the seeds also mature.
Fruits may be classified as simple, aggregate, multiple, or accessory, depending on their origin Figure 3. Your browser does not support JavaScript. To use all the functions on Chemie. DE please activate JavaScript. References Mirov, N. The Genus Pinus. Ronald Press Company, New York. Farjon, A. Pinus Pinaceae. Flora Neotropica Monograph It uses material from the Wikipedia article "Cotyledon". A list of authors is available in Wikipedia. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants angiosperms.
Species with one cotyledon are called monocotyledonous or, "monocots" and placed in the Class Liliopsida. Plants with two embryonic leaves are termed dicotyledonous "dicots" and placed in the Class Magnoliopsida. Reference Terms. Upon germination, the cotyledon usually becomes the embryonic first leaves of a seedling. Related Stories.
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