Chapter 23, Problem 43A

Summary Introduction

To write:

About the long-day plants flowers

Introduction:

Certain plants flowered only at certain times of the year. The researchers focused on the number of hours of daylight to which the plants were exposed. They also discovered that the critical factor that influenced flowering was the number of hours of uninterrupted darkness, not the number of hours of daylight. This flowering response is called photoperiodism. They also learned that the beginning of flower development for each plant species was a response to a range in the number of hours of darkness. This range of hours is called the plant’s critical period. Based on the critical period, botanists classify flowering plants into one of four different groups.

Explanation of Solution

Based on the critical period, botanists classify flowering plants into one of four different groups.

A long-day plant flowers when the number of hours of darkness is smaller than its critical period. These plants flower during the summer. The examples of long-day plants are asters, spinach, coneflowers, and potatoes. Spinach has a critical photoperiod of 13 hours.

Conclusion

Therefore, it can be concluded that plants which only flower when the length of the day rises above a certain threshold are said as long-day plants.