INTRODUCTION

Plants not only use day to night transition to time repeated functions from day to day (see Chapter 8) but also to measure the seasons of the year. Down the centuries humans have used leaf, flower, and fruit production by local plants as signals for seasonal activities such as when to begin planting crops or when to harvest. The agriculturalists Garner and Allard (more about whom shortly) expressed it this way:

PATTERNS OF GROWTH

Away from the tropics

In temperate climates there is a pattern of plant growth arranged around a yearly period of relative inactivity, winter. The pattern is seen most clearly in annuals, which grow and reproduce during favorable weather and spend winter as seeds.

Other kinds of plants also have distinct patterns of growth. Herbaceous perennials produce annual stem growth which ceases well before winter; deciduous shrubs and trees lose their leaves in the fall but begin preparing for that event well in advance of winter. In all cases of periodic growth, some signal causes the plant to go from rapid growth to near complete shutdown in days or weeks.