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CHAP. XXIV. CARBOHYDRATE-FORMATION 



£1 



were employed ; of this v is always kept inside the balance- 

 room at the constant temperature. The second vessel V, 

 is used for exposing the plant to light and for collecting the 

 evolved oxygen. A specimen of the plant bearing about 

 forty leaves is cut the previous night and placed (with the 



hook and the waxed cocoon 

 thread) in the second vessel 

 Vi. This specimen is exposed 

 to light in the morning till 

 bubbling takes place. The 

 intercellular spaces are then 

 filled with oxygen, the excess 

 escaping at the cut end. The 

 vessel Vx is now taken into 

 the balance-room, and the 

 plant transferred to the vessel 

 v and suspended from the 

 balance by the hook. The 

 plant immersed in water is ex- 

 actly balanced by a counter- 

 poise placed in the second pan, 

 and by means of the rider the 

 long index is adjusted to the 

 zero of the scale (fig. 53). 

 There may be a misgiving 

 that the plant might get 

 Fig. 54. Eudiometer e for coilec- partially dried during transfer 



Light** ° Xygen eV ° 1Ved Und6r from one vessel t0 the other ' 

 v 1; second vessel ; h, suspending thus resulting in a slight 



hook - variation of weight. There 



is, however, no ground for this misgiving, as was proved 

 by lifting the plant by the hook out of the vessel and 

 reweighing it five times in succession. This did not 

 produce the slightest variation in the weight, the index 

 remaining exactly at zero. The plant, it must be remembered, 

 is coated with a film of water which prevents contact with 

 the air. The precaution of raising the plant and reweighing 



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