HI 



r\ 





/ 





- - 



- 



.: 1 



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in a CN'lindcr containinj^ aquatic plants. The test-tube is filled with 

 water and, as the yas collects, the water is displaced. After i 5 

 or more cc. of gas is collected, the 

 funnel is dropped into the cylinder 

 and a stick of phosphorus, fastened 

 to a bent wire, shown at the right, is 

 inserted into the tube containing the 

 gas. The phosphorus should be left 

 in the tube for some hours, and 

 after removing it the difference in 

 the water levels is noted and the 

 per cent, of oxygen is roughly de- 

 termined. In most experiments, 

 our students find that about 33 per 

 cent, of the gas is absorbed by the 

 phosphorus. 



Method of Determining Hourly 



Tr.anspiration ''"=■ ^- ,^'^^'^°^ °f ^°^'f '"8 



and testing the gas given ofT by 

 The following method of deter- aquatic plants. 



mining the hourly transpiration of 



rooted plants has been occasionally employed in our labo- 

 ratory. The device consists of a calcium chloride jar, to which 

 is attached a small tube, both of which contain water. See Fig. 5. 

 A small light float of pith attached to a straw, carrying a wire 

 on its upper end, registers on a blackened cylinder the variation 

 of the water level due to transpiration. On the surface of the 

 column of water in the small tube there are a few drops of heavy 

 paraffine oil, o. This oil prevents loss, of water, and serves as a 

 suitable rider for the float. In our demonstration experiments 

 we make use of willow cuttings which have developed roots and 

 leaves. These cuttings are started in water and as soon as gath- 

 ered they are fitted with a rubber stopper of suitable size to fit 

 the calcium chloride jar. Rooted willow cuttings are far superior 

 to fresh cut stems and leaves in this experiment on account of 

 the ends of the latter becoming clogged with slimy material, thus 

 preventing absorption and rendering the results of little \alue. 



