io6 



THE VEGETATIVE FUNCTIONS OF PLANTS 



observation justifies the inference that living plants 

 take in oxygen. 



107. Carbon Dioxide Given Off. The air in each of 

 the seven cylinders may next be tested with lime-water, 



by pouring in not more than 

 ong or two tablespoonfuls, and 

 mixing it well with the air by 

 tipping the cylinders, holding 

 the halves with the plant ma- 

 terial uppermost, and allowing 

 the lime-water to flow back 

 and forth a few times from one 

 end of the jar to the other. 

 Care should be taken not to 

 dirty the lime-water by allow- 

 ing it to rinse the plant mate- 

 rial. After this treatment the 

 lime-water will be found to 

 have turned milky in all of the 

 jars except the one containing 

 no plant tissue. From these 

 results we may correctly infer 

 that carbon dioxide has been 

 given off by the plants. 



108. Heat Evolved. That 

 heat is evolved during the 

 gaseous exchange above 

 demonstrated may be illus- 

 trated by placing a delicate 

 thermometer into, say, the germinating seeds. The best 

 results will be obtained by placing the plant material into 

 a double- walled Dewar flask (or a thermos bottle), which 



FIG. 69. A simple calorim- 

 eter for studying the tempera- 

 ture transformations in respira- 

 tion. Respiring seeds are placed 

 in the Dewar bulb (double walled, 

 with a vacuum between the 

 walls). At the bottom of the 

 bulb is a dish containing caustic 

 potash; cotton wool is packed 

 between the thermometer and 

 the neck of the bulb. (After 

 Ganong.) 



