THE MOLECULAR FORCES IN PLANTS. 161 



IV. THE MOVEMENT OF GASES IN PLANTS. 

 64. Concerning the Behaviour of Gases in General. 



A test-tube is filled with plant juice, e.g. beetroot juice, 

 obtained by rubbing pieces of peeled beetroot on, a grater, 

 squeezing the pulp in a cloth and finally clearing by filtration. 

 We also fill a small dish with the beetroot juice, invert the test- 

 tube in it, and then replace the juice in the test-tube by Carbon 

 dioxide gas. If we let the apparatus stand for some time, we 

 shall observe that the juice rises in the test-tube. The Carbon 

 dioxide is absorbed by the fluid, and in the same way the sap 

 present in the intact cell is able to absorb Carbon dioxide gas 

 brought into contact with it. Oxygen and Nitrogen are absorbed 

 by aqueous solutions much less energetically than Carbon dioxide 

 gas. 



Air-dry plant structures, e.g. seeds, can also absorb not incon- 

 siderable quantities of Carbon dioxide. In a glass tube fused up 

 at one end, we place 15 to 20 air-dry seeds of Phaseolus multi- 

 florue, and then push in a small piece of cork or some glass 

 wool, so as to confine the seeds to the closed end of the tube. 

 The tube is now placed with its closed end downwards, a rapid 

 current of Carbon dioxide is led into it, and it is then closed with 

 the thumb and quickly inverted with its mouth under mercury. 

 The mercury gradually rises in the tube, the seeds in the course 

 of several days absorbing some cubic centimetres of Carbon 

 dioxide, and if we accurately determine the volume of the gas at 

 the beginning and at the end of the experiment respectively (see 

 method in 13), we can estimate exactly the amount of Carbon 

 dioxide fixed by the seeds. 1 According to Borodin, soaked bean 

 seeds absorb not much more Carbon dioxide than air-dry seeds, a 

 statement which challenges further investigation. 



As shown by Graham and Bunsen, the rate at which gases 

 traverse in opposite directions porous septa which exert no 

 specific force or attraction on these gases, varies inversely as the 

 square root of the specific gravity of the gases. Indeed, it may 

 easily be shown that Hydrogen, e.g., passes much more rapidly 

 through porous partitions than does atmospheric air. In. my 

 experiments I used a glass tube 15 mm. in diameter and about 

 40 cm. long, closed at one end with a dry plate of clay 5 mm. in 

 thickness. The clay plate may be easily fixed on the end of the 

 tube with sealing-wax. If the glass tube is now filled with 

 P.P. M 



