CONTENTS 



Page 



Introduction 1 



Light and seed germination 1 



Light and plant growth 2 



Light and plant pigments 3 



Effect of duration of light on plants 3 



General cultural hints 5 



General references 5 



Demonstrations 



A. Light and seed germination 



1. Effect of light on germination of seeds planted in soil 6 



2. How to test various kinds of seeds to determine their light requirement for germination 7 



3. Effect of duration of imbibition period (soaking) on effectiveness of a given light exposure in 

 promoting germination of light-sensitive seeds 8 



4. How a light requirement for germination can be induced in seeds that normally do not require 



light for germination 9 



5. Photoreversible control of seed germination by red and far-red light 10 



B. Light and plant growth 



1. Control by light of the growth of an internode 11 



2. Control by light of growth and chlorophyll formation 11 



3. Why plants bend toward light (phototropism) 12 



4. Effect of red and far-red light on elongation of stems of light-grown plants 12 



C. Light and plant pigments 



1. Effect of light on formation of anthocyanin in seedlings 13 



2. Effect of light on tomato skin and fruit color 14 



3. Localization of response to tight by the pigment in tomato skin 15 



4. Effect of light on coloration of apples 15 



D. Duration of light 



1. Photoperiodic control of flowering of short-day plants 16 



2. Photoperiodic control of flowering of long-day plants 17 



3. Photoperiodic control of growth and dormancy of woody plants 17 



4. Photoperiodic control of bulb formation of onions 18 



Washington, D.C. Revised March 1966 



For sale by the Superintendent of Documents, U. S. Government Printijig Office 

 Washington, D.C. 20402 



