62 THE NATURE AND WORK OF PLANTS 



dow glass and red tissue paper, and the other with 

 glass and blue paper, and set in a sunny place. Care 

 for the plants from day to day, and compare their 

 growth at the end of a week. This will determine 

 whether the blue or red rays -are most useful to 

 the plant, and will also recall the mistaken "blue 

 glass " craze of a few years ago. 



71. LigJit destroys chlorophyl. — Place a portion 

 of the solution of chlorophyl prepared in § 67 in 

 the sunlight, and the remainder in a dark closet. 

 Compare the color of the two in a few days. The 

 one in the light will be seen to have faded. The 

 fading action of light goes on in the leaf con- 

 stantly, but the green color is constantly restored 

 by the protoplasm. If a plant should be exposed 

 to a light much stronger than that to which it is 

 accustomed, the fading will take place faster than 

 the living matter could mend it, and the leaf would 

 turn yellow and die. 



72. Light is necessary for the formation of chlo- 

 rophyl in most instances. — While light slowly breaks 

 down chlorophyl, yet the plant usually cannot form 

 its substance without the aid of light. Place a 

 bulb of canna, jack-in- the-pulpit, or a seed of the 



