FIGURE 24–11 Germination: A Comparison The monocot corn seedling (left) grows directly upward, protected by a sheath of tissue that surrounds the developing leaves. In contrast, the garden bean (right) forms a hook in its stem that gently pulls the new plant tissues through the soil. Predict What might happen to a germinating seedling that lacked such adaptations?
Advantages of Dormancy Seed dormancy can be adaptive in several ways. For one, it can allow for long-distance dispersal. And it also allows seeds to germinate under ideal growth conditions. The seeds of most temperate plants, for example, germinate in the spring, when conditions are best for growth. For some species, a period of cold temperatures during which the seeds are dormant is required before growth can begin. Seeds can easily survive winter cold, but many young green plants cannot. The period of cold that is required is long enough that seeds will not germinate until the dangerous winter season has passed.
Sometimes, only extreme environmental conditions can end seed dormancy. Some pine trees, for example, produce seeds in cones that remain sealed until the high temperatures generated by forest fires cause the cones to open. The high temperature both activates and releases the seeds, allowing the plants to reclaim the forest quickly after a fire.
24.2 Assessment
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Review Describe how fruits form.
Infer Is a pumpkin a fruit? Describe any evidence you use in making your inference.
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Review Describe two methods of seed dispersal.
Pose Questions A new angiosperm species is discovered. What questions would you ask before predicting how its seeds are dispersed? Explain the rationale for asking each question.
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Review Summarize the environmental factors that affect seed germination.
Explain Why is it adaptive for some seeds to remain dormant before they germinate?
Apply Concepts The seeds of a bishop pine germinate only after exposure to the extreme heat of a forest fire. Evaluate the significance of this structural adaptation.
WRITE ABOUT SCIENCE
Imagine that you are writing a children's book about seeds and that you are working on the chapter on dispersal. Write from one to three paragraphs on seed dispersal by wind. Hint: Try to include details that you would have found appealing when you were about eight years old.
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis