4 6 



EXPERIMENTAL PLANT PHYSIOLOGY. 



loss of heat as far as possible, cover the funnel with a perforated 

 glass plate, whereby access of air is prevented. The carbon dioxide 

 FIG. 41. formed is absorbed by a solution of 



potassium hydrate which is placed in 

 a glass dish under the funnel. As a 

 comparison place near this apparatus 

 a thermometer in the free air which 

 will not be affected by the heat of 

 the plants. To obtain the most uni- 

 form temperature for both thermom- 

 eters cover each with a large bell-jar. 



37. Respiration, Essential to 

 Growth, and Dependent on Air. The 

 conversion of food into living sub- 

 stance is possible by means of 

 respiration only. The higher plants 

 may carry on a certain amount of 

 intramolecular respiration and thus 

 accomplish a small amount of 

 growth. For the normal development of the plant, however, 

 it is necessary that it have access to the free oxygen of the air. 

 EXPERIMENT 54. 



OXYGEN NECESSARY FOR RESPIRATION. 



Ap a?ion tU o1 

 (Sachs.) 



Fill two respiration-tubes of 100 cc. 

 capacity with water which has been 

 boiled to drive off the dissolved air. In 

 the bulbs of each insert a half-dozen 

 seeds of Pea or Wheat, and invert over 

 a dish of mercury. Twenty-four hours 

 later displace nearly all of the water in 

 one tube with hydrogen and the other 

 with air. The seeds in hydrogen do not 

 germinate, while those in air, which are 

 able to obtain their customary supply of 

 oxygen, develop normally. To obtain 

 the hydrogen, place a few grams of gran- 

 ulated zinc in a flask or bottle, and cover 



FIG. 42. 



Respiration-tubes. (Detmer.) 

 A, filled with hydrogen, 

 and , oxygen. 



to a depth of 5 cm. 



