5. Other Growth Regulators and Seasonal Responses

Responding to day length and night length

Plants can be divided into three groups, depending on their response tot he photoperiod, which again acts a season indicator.

One group, called day-neutral plants (DNPs) are not affected by day length. Examples of DNPs for flowering include tomatoes, dandelions, roses, corn, cotton, and beans.

Short-day plants (SDPs) flower in the spring or fall, when the day length is short. For example ragweed flowers when the days are shorter than 14 hours and poinsettias flower when the days are shorter than 12 hours. Chrysanthemums, goldenrods, and soybeans are SDPs for flowering.

Long-day plants (LDPs) flower when the days are long, usually in summer. For example, wheat flowers only when the days are longer than 10 hours. Radishes, asters, petunias, and beets are LDPs for flowering.

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