16 



ACIDITY AND GAS INTERCHANGE IN CACTI. 



condition it was a simple matter to expel the gas in the pipette into the vial 

 until the latter was from half to two-thirds full of the sample. If the analysis 

 was not to be made at once a stopper was very tightly jammed into the mouth 

 of the vial and it was then placed in a case where it could not possibly fall on its 

 side. The gas, under some compression, had a seal of 8 to 10 mm. of mercury 

 below it, so that it could stand considerable rough handling without bringing 

 the gas in contact with the stopper itself. These samples that were brought 

 back to New York were kept carefully in an upright position during transit. 



After the samples had been removed the capacity of the flask with the cactus 

 joints still in it was determined by direct measurement and the material itself 

 used for an acidity determination and later for the estimation of dry weight. 



In the summer of 1913 an extended series of experiments was made under 

 various conditions. In these the samples were obtained and capacity of the 

 flasks were determined by an improved method. The apparatus used for this 

 was modeled after that devised by Aubert" with a few modifications. Follow- 



FIG. 1. Apparatus for obtaining gas samples. 



o=receiver; about 750 c.c. capacity. 



b = delivery tube. 



c =manometer. 



d = thermometer. 



e= rubber connector; wired. 



/=bulb of sampling apparatus: 25 c.c. 



capacity. 

 g = rubber tube connecting with mercury 



reservoir. 



h = deli very tube of sampling apparatus. 

 i =mercury bath. 



The attachment for determining capacity of receiver was simply a large bulb of about 75 c.c. 

 capacity, attached to the delivery tube b in the same way as shown above. 



"Aubert, E. Recherches physiologiques sur les plantes grasses. 2d part, p. 11, 1892. See also 

 Abderhalden, Handbuch d. Biochem. Arbeitsmethoden, vol. 3, p. 501. 



