INFLUENCE OF ILLUMINATING GAS 45 



protoplasm to accommodate itself so perfectly that movement 

 may continue for some time in a pure gas. 



For the determination of the length of time and concentra- 

 tion in which the pollen will germinate (See chemotropism of 

 pollen) place a number of pollen cells in the proper culture solu- 

 tion on a cover-glass and invert over an Engelmann gas chamber. 

 Expose to the mixtures as above, and note the influence of this 

 compound upon the formation of the pollen tubes. l 



60. Growth in Oxygen. Make a supply of pure oxygen by 

 heating a mixture of potassium chlorate and manganese dioxide 

 in a retort connected with a gasometer as above, or secure a 

 supply of the gas from a factory in steel cylinders. 



Test for purity (See text-books of chemistry). 



Mount material showing movement of the proto- 

 plasm, and then expose to mixtures of air containing 

 increased percentage of oxygen, and to the pure gas. 

 Is the movement accelerated ? Soak a dozen seeds 

 of wheat or corn in water for 24 hours, and then place 

 a half dozen of each in two 10 cm. test-tubes. Push a 

 partition of wire gauze to within 3 cm. of the bottom. 

 Fill the tubes with water and fasten in an inverted FlG 

 position with the mouth of the tube in a dish of mer- Respiration 

 cury. Now displace the water in one tube with air, tube > A > 

 and the other with pure oxygen. Note results 24, 48, ^"^T'^ 

 and 72 hours later. Repeat, using different percent- se eds rest- 

 ages of oxygen. Is the rate of growth of the germi- ing on wire 

 nating seedling accelerated by increasing the pressure j 

 of the oxygen ? 



61. Influence of Illuminating Gas. The illuminating gas used 

 in cities generally consists of a mixture of marsh gas and volatile 

 petroleum products. This mixture escapes from the pipes and 

 fills up the air-spaces in the soil, displacing the oxygen and 

 exerting its own proper effect upon the plants which send their 



1 Lopriore, G. Ueber die Einwirkung der Kohlensaure auf das Protoplasma der 

 lebenden Pflanzenzelle. Jahrb. Wiss. Bot. 28 : 531. 1895. 



