Exchange and Movements of Gases and Liquids. 79 



j^irect connection between the cortical air spaces and the air. 

 In the case of deciduous plants, the stomatal openings are lost 

 in winter or during the resting season, the leaf-scars sealed with 

 cork, and the lenticels are also more or less 

 completely closed. 



The large chambers found in many stems, 

 such as those of the grasses and of other 

 plants produced by the rupture of the pith, 

 are results of growth and of the mechanical 

 necessities of construction, rather than to 

 meet any need for aeration. 



75. Air passages through steins 

 and leaves. — Provide a small bottle with 

 a tightly fitting stopper, and fill it about 

 half full of water. Fit the petiole of a leaf 

 of Ptimiila or Primus in the stopper, and 

 seal tightly with gelatine which has been 

 soaked in water for an hour. Thrust a short 

 section of glass tubing, bent at right angles, 

 through a second hole in the cork. ^Vith 



the mouth apply strong suction to the tube until bubbles are 

 seen to pour from the end of the petiole which is submerged. 

 Continue the process until it is ascertained whether the 

 bubbles come from air in the stem, or air is drawn through 

 the leaf. 



76. Passage of air through lenticels and cortex. — ■ 

 Examine a branch of Salix, Sambucus, Syringa, or Populus, 

 and note the number of roughened elevations to be seen on 

 the bark. Cut a section of sufficient length to pass through 

 the stopper, and beneath the surface of the water, in the ap- 

 paratus described in the above test. Seal the upper end of the 

 branch with wax, and fit tightly in the cork, as above. Now 

 apply suction, and ascertain whether air may enter the lenticels 

 and come out from the lower end of the twig. The bottle 



Fi&. S5- — Portion 

 of branch of an oak, 

 showing lenticels. 

 After Bonnier and 

 Leclerc du Sablon. 



