Nutrition. 



cipitate is redissolved. This will permit, cliiefly, red and 

 yellow rays to pass in one preparation, and blue-violet in 

 the other. Now make up two 

 preparations of algae, or aquatic 

 plants, as in §93, and set inside of 

 each inner cylinder, and cover the 

 top with some opaque body, so that 

 only the light which has passed 

 through the solutions may strike 

 the plants. Set in sunlight. Note 

 amount and quality of gas collect- 

 ing in the tubes in the two in- 

 stances. Care must be taken that 

 the same amount of material is 

 placed in the two test tubes 

 (Fig. 60). 



Double- walled bell jars may be 

 obtained, which facihtate the per- 

 formance of this demonstration. 



A box with blackened inner sur- 

 faces, and the open ends suitable 



for holding sheets of ruby, yellow, and blue glass, may also be 

 used to expose plants to a portion of the spectrum (Fig. 63). 



95. Relations of plants and animals to the atmos- 

 phere. — Enclose two or three living mice in a small wire 

 cage, and place on a ground-glass plate of the proper size to 

 receive a bell jar. Invert a large bell jar, and fill it loosely 

 with fresh, leafy shoots, or set a plant with many leaves beside 

 the cage. Place the bell jar over the cage, and seal to the 

 plate with vaseline. The cage should be in such position that 

 the animals may be easily observed through the glass. Place 

 the whole preparation in a dark room, or cover completely with 

 a photographer's focussing cloth, to exclude the light. Note 

 the condition of the mice at the end of a period of half an 



Fig. 62. — Bell jar with double 

 walls, for testing effect of colored 

 light on liberation of oxygen. 

 After Sachs. 



