ON THE RESPIRATORY FUNCTION OF STOMATA. 27 



In the second reading we have the C0 2 of respiration 

 made evident, but this in the first reading is wholly as- 

 similated. 



This and other similar estimations show conclusively 

 that the classical experiment by Garreau (14) demonstrating 

 the liberation of carbon dioxide in bright light is misleading. 

 That a little CO. continually escapes from an entire branch 

 put in a closed chamber with baryta water in the sun is not 

 to be wondered at. The shaded parts of assimilating tissues, 

 together with the non-assimilating tissues of petioles, stems, 

 buds, etc., might quite account for this, but it is difficult to 

 see how any carbonic acid should escape from a completely 

 illuminated leaf surface of normal assimilatory activity. The 

 result of Garreau's experiment is then only an expression of 

 the uncritical conditions in which it was made. Corenwinder 

 (15) showed in 1878 that with young but expanded leaves 

 the chlorophyll of which was not yet fully developed, an 

 evolution of carbon dioxide takes place in the sun, and that 

 this is clearly due merely to the imperfect development of 

 the assimilatory function, for the amount of the C0 2 liberated 

 increases in the dark. With mature leaves he found that 

 no liberation of C0 2 takes place in sunshine. 



ON THE GASEOUS EXCHANGE IN LEAVES WHEN THE 

 STOMATA ARE OCCLUDED. 



As I have stated above Boussingault has been generally 

 held to have proved that during assimilation C0 2 is taken 

 up chiefly by the epidermis cells of the upper leaf surface 

 which directly adjoin the assimilating palisade cells. He 

 arrived at this conclusion by taking two similar leaves of 

 Oleander, coating the upper surface of one and the under 

 surface of the other with lard, and then exposing them to 

 light in vessels containing known amounts of CO. and 

 air. He found that whereas the one assimilated 10 c.c. of 

 C0 2 the other with its stomata blocked assimilated 17*5 c.c. 

 He drew the obvious conclusion that the upper stomata- 

 less surface is the chief seat of absorption and that it is the 

 coating of this with lard that reduces the assimilation to 

 10 c.c. of CO. in the first case. 



