Some kinds of seeds require special treatment to initiate germination. Those having impervious seed coats may be soaked in concentrated sulfuric acid for several minutes and then thoroughly washed with water in an effort to make the coats permeable. Another approach is to dip such seeds in scalding water. Timing of such treatments is critical.
Light is important in germination. Some kinds of seeds will not germinate when buried in soil because they require exposure to light after having absorbed moisture. They therefore must be brought to the surface.
Germination of light-sensitive seeds is promoted by red light but inhibited by # Notes # far-red light.
While some seeds are able to germinate as soon as they are mature, many seeds first require a conditioning treatment, most commonly, a period of low temperature. This makes sense because otherwise, seeds would germinate in the fall and the resulting delicate seedlings be killed by winter conditions. Supplying low temperature, a process known as cold stratification, is done in conjunction with moisture. In nature, this means overwintering; otherwise seeds can be put in sphagnum moss with moisture and stored in the refrigerator. Honeysuckle requires 30 to 60 days of such treatment, pears 60 to 90 days, hemlock 60 to 120 days. During this period of low temperature, a number of biochemical and physical changes occur before the seeds gain the capacity to germinate. Another name for cold stratification is vernalization. This name is also used in reference to high-temperature treatment, though less commonly so. Vernalization is practiced on cereal grains more often than on other types of seeds. It is especially significant for winter wheat, given that the treatment speeds the life cycle and thus allows the seeds to mature in northerly climates. The turkey red variety of winter wheat can be first soaked in water to raise the moisture content to 60 percent and then treated at 33 to 37°F for nine weeks or more. Grain can thus be grown to maturity in approximately thirty days. Such grains can be grown in Siberia. In fact, another name for the process honors a Russian scientist: Jarovisation.
Germinating seeds also require oxygen. The soil in which seeds sprout should be well aerated and porous. Careful attention must be given to watering.
Germinating seeds are often damaged by fungi residing in the soil. It is sometimes necessary, therefore, to either sterilize soil in an autoclave or treat soil with a disinfectant such as bichloride of mercury or formaldehyde. In addition, seeds can be coated with zinc oxide or mercury or copper compounds to minimize loss from fungi and bacteria.
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