2174 Journal of Applied Microscopy 



Methods in Plant Physiology. 

 VIII. 



CARBON ASSIMILATION.— Continued. 



12. Identification of the Gas Produced in Carbon Assimilation. The gas which 

 is produced as a by-product in photosynthesis may be easily collected and identi- 

 fied as oxygen, if a sufficient quantity is obtained. 



Fill a jar with water to within a few centimeters of the top; select a fun- 

 nel whose diameter and height are a little less than those of the jar. Into the 

 funnel place a dozen vigorous stems of Elodea canadensis, or other water plant, 

 and sink the funnel, bowl downward, into the jar of water, including all of the 

 plant material within the funnel. Fill a test tube with water and, without 

 admitting any air, set it down over the submerged stem of the funnel. Keep 

 the jar in sunlight until the test tube is nearly full of gas, then, without raising 

 the mouth of the tube above the water, detach it from the funnel and cover the 

 open end with the thumb. Test the contents of the tube with a glowing 

 splinter. 



13. The Evolution and Absorption of Gases in Carbon Assimilation, {a) Bous- 

 singaulfs Phosphorus Method.-— Y'lW a tall bell-jar over water with hydrogen and 

 carbon dioxid, the latter should compose 8 to 10 per cent, of the mixture. It 

 is best to keep the bell-jar and water in a large pan which will admit of being 

 easily transported. Place a small potted plant, c. g., a Coleus, under the bell- 

 jar before any gases are admitted. Attach a small piece of phosphorus to a 

 curved wire and introduce it under the bell-jar, allowing it to project above the 

 surface of the water. The oxygen in the intercellular spaces of the plant will 

 unite with the phosphorus, filling the bell-jar with the white fumes of the P2O3. 

 Place the preparation in the dark until the fumes have been absorbed by the 

 water, which will occur in two or three hours ; then place the bell-jar in strong 

 light, noticing how quickly the white fumes reappear. 



(p) Pfeffer''s Method for Estiviaiing the Quantity of Carbon Dioxid Consumed 

 in Photosynthesis. — This experiment consists in exposing a leaf to light in an at- 

 mosphere containing a known amount of carbon dioxid and actually measuring the 

 amount consumed. The necessary apparatus is shown in Fig. 8 ; the glass tube 

 is 15 mm. in diameter and about 100 cm. long, the upper end is blown out into a 

 balloon. The open end of the tube dips into a dish of mercury. Attach a fine 

 wire to the petiole of a leaf of Neriuni oleander, roll the leaf into a cylinder and 

 thrust it up the tube until it reaches the wide part, where it will unfold of itself. 

 The tube is held in position over the mercury by means of a burette holder. A 

 few drops of water are placed above the mercury column in the tube to protect 

 the leaf from vapors of mercury. By means of a curved pipette remove some 

 of the air from the tube, thus causing the mercury to rise a short distance. 

 Record the volume of the air in the calibrated tube, also the height of the little 

 column of water in the tube. Readings of the barometer and thermometer are 

 also taken. 



