RELATIONS OF PLANTS TO GASES 



191 



gases are drawn in by filtration pressure. Repeat the experiment, 

 and suspend a small dish of water near the top of the tube, from 

 which a strip of filter paper runs to the membrane and keeps it 

 moist. In an experiment by the author a grape skin permitted 



91 92 



Fig. 91. Demonstration of the passage of air through stomata, spongy parenchyma 

 of leaf, and cortex of petiole. G, small bottle containing distilled water in which is 

 immersed the lower end of a freshly cut petiole of Primula Sinensis. R, tube through 

 which the air in the bottle is exhausted. After Detmer. 



Fig. 92. Diagram of force and blast pump, to be used in drawing or forcing air 

 through leaf. 



the diffusion of carbon dioxide to lift a column of mercury 26 

 cm. in height, which was maintained 14 months. 



264. Diffusion Through a Waxy Membrane. Repeat experi- 

 ment as above, using the thick waxy skin of a " winter " apple, or 

 a skin of a grape. Note the steady rise of the column through 



