METABOLIC PROCESSES IN THE PLANT. 



2G1 



support, 7f, hang two tubes which dip at the bottom into water 

 contained in the beakers G, G'. The narrower parts A, B of the 

 tubes, about 45 cm. in length and 15 mm. in diameter, are accu- 

 rately calibrated to O2 c.c. The upper portions W, W' t 30 cm. 

 long and 40 mm. in diameter, are closed with well-fitting, care- 

 fully selected rubber stoppers, through each of which passes a 

 glass tube provided with a well-greased glass stop-cock, h, h'* The 

 short, wide glass test-tube seen in one of the tubes is suspended by 

 a wire, and contains clear concentrated potash solution. Into each 

 tube are now introduced, say, twenty-five pea seedlings, three 

 days old, and grown at 15 C. They are placed in the upper 

 widened part of the tubes, on moist glass wool. We put the 

 apparatus in a place where the temperature is very constant, suck 

 up some water into the lower portions 

 of the tubes A and B, close the stop- 

 cocks, and at the end of, say, half an 

 hour, read off the position of the 

 water in A and B. We observe also 

 the temperature indicated by the 

 thermometer T. In an experiment 

 made by me with twenty-five pea 

 seedlings at 15 C., the water in the 

 tube provided with potash solution 

 rose in twenty-one hours from 22' 2 

 c.c. to 6O4 c.c. In the tube, on the 

 other hand, without potash solution, 

 if the temperature is kept approxi- 

 mately constant, the level of the 

 water changes very little, because 

 the Carbon dioxide produced in re- 

 spiration appears bulk for bulk in 

 place of the Oxygen used up. In 

 presence of potash the water must 

 rise, because the Carbon dioxide 

 produced by the plants is rapidly 

 absorbed, and does not replace the 

 Oxygen consumed. 



In the following demonstration 



-. -i , i FIG. 94. Apparatus for experiments 



experiment also water may be used on plant relation. 



* Instead of the rubber stoppers we may employ ground glass stoppers. 



