Chapter 29.6, Problem 13SAQ

Summary Introduction

To explain:

The reason behind non-flowering of the short day plant until late summer which germinates in spring and reason behind not flowering of the long day plant that germinates at end of summer till late spring.

Introduction:

The flowering in flowering plants is dependent on the day length. The effect of the photoperiod on flowering is termed as the photoperiodism. The short day plants are those plants which flower only when the light period is below the critical value. The long day plants flowers when they get light for more than a certain length.

Explanation of Solution

The photoperiodism ensures that the flowering takes place only when the size of plant is appropriate to support the development of seeds. The photoperiodism also ensures that the seeds mature before adverse environment such as winter approaches. A short day plant germinates in the spring and do not flower till summer because the day length is less than the critical value. This allows the plant to grow in size and switching to produce flower in order to complete the development of seed before winter.

In long day plants, the flowering takes place in the mid-summer as they get optimal light period. The long day plants germinate in spring and flowers when the length of the day exceeds the critical limit. In some of the plants, flowering take place only when the plants has experienced long period of winter, this is known as vernalization. The vernalization prevents the long day plant to flower in the summer and forces the plant to flower in spring when there are high chances of pollination and development of seeds.

Conclusion

The flowering of the plant is dependent on the photoperiodism and the size of the plant. The short day plant germinates in the spring; however, they are not able to flower because of the small size even when the daylight period is optimal. They flower late summer when they acquire optimal size. The long day plant germinates at the end of summer and flowers when the light is optimal. The vernalization prevents some of the long day plants to flower in the summer.