192 



MOVEMENTS AND EXCHANGES OF FLUIDS 



a long period and its ultimate maintenance at the maximum ele- 

 vation. Such membranes contain but little water of imbibition 

 although sufficient to allow diffusion. This amount is not lost by 

 desiccation, so the membrane continues to act osmotically and 

 does not become cracked, or permeable to gases under filtration 

 pressure. 



265. Diffusion of Gases Through Leaves. Repeat experiment 

 as above, using leaves of Ficus, oak, or any convenient plant with 

 a firm leaf. The section of the leaf should be fastened to the 

 apparatus with the edges sealed to prevent the passage of gas 

 through the intercellular spaces into the air. 



266. Connection of Air in Cortex and Spongy 

 Parenchyma of Leaves with the Atmosphere 

 Through the Stomata. Fit a leaf of Primula 

 Sinensis, or Prunus, to a stopper by boring a 

 suitable hole through the stopper and passing the 

 petiole through it, then sealing with gelatine or 

 wax. Bore a second hole through the stopper 

 and insert a short section of tubing bent at right 

 angles. Force the stopper into a bottle of proper 

 size half full of water. Connect tube with filter 

 pump cr suck with the mouth. Note the streams 

 of bubbles pouring from the end of the stem. 

 Continue until it is demonstrated that the bubbles 

 are produced by air passing through the leaf and 

 petiole, not by expansion of the gases in the in- 

 tercellular spaces. If the leaf is submerged, and air forced into 

 the petiole by blowing with the mouth, or force pump, bubbles 

 may be seen to arise from the surface from the air coming 

 through the stomata. The openings of the stomata soon become 

 filled with water, after which the passage of air may not be 

 demonstrated (Fig. 91). 



267. Connection of Air in Cortex of Branches with Atmosphere 

 through Lenticels. Examine a branch of Salix, Sambucus, Syr- 

 inga, or Populus, and a number of small, rough areas slightly 



Fig. 93. Por- 

 tion of branch of 

 oak showing len- 

 ticels. After Bon- 

 nier and Leclerc 

 du Sablon. 



