1902.] 



Influence of Carbon Dioxide on leaves, etc. 



401 



the increased amounts of CO2 in the air passed over the leaf being evi- 

 dently in excess of the power of the assimilatory centres to deal with 

 them. In such cases the ratios of intake are necessarily considerably 

 lower than the ratios of the partial pressures. 



Experiment III. Under Insufficient Illumination. — In this instance the 

 day (August 29, 1899) was very cloudy, with rain falling during 

 nearly the whole time. 



Cut leaves of Helianthus annum A and B were placed in adjoinin 

 •cases as in the other experiments. 



Leaf A. 



Area of leaf 275 - 9 sq. cm. 



Air passed in 3i hours (N.T.P.) 287 "94 litres 



1 hour 88-5 „ 



C0 2 content of air entering case 2 *80 parts per 10,000 



leaving „ 1*70 „ „ 



Mean C0 2 content of air in contact with leaf 



during experiment 2 '25 „ 



C0 2 absorbed by leaf per hour 9 '7 c.c. 



„ per sq. metre per hour 351 c.c. 



Leaf B. 



Area of leaf 411 *2 sq. cm. 



Air passed in 3J hours 248 '17 litres. 



„ 1 hour 76-3 „ 



C0 2 content of air entering case 21 *3 per 10,0C0 



., „ leaving „ 11-5 „ 



Mean C0 2 content of air in contact with leaf 



during experiment 16 '4 



COo absorbed by leaf per hour 74 '8 c.c. 



per sq. metre per hour 1819 c.c. 



Eatio of partial pressures of C0 2 in A and B, 2-25 : 16*4 = 1: 72. 

 Eatio of COo absorbed per square metre per hour in A andB, 351 : 1819 

 = 1:51 



Experiment IV. — A similar experiment under insufficient illumination 

 on leaves of Catalpa bignonioides, August 31, 1899. The sky was very 

 dark, with some rain, and only a few gleams of partial sunlight near 

 the close of the experiment. 



Leaf A. 



Area of leaf 417 '6 sq. cm. 



Air passed in 4 hours (N.T.P.) 304 '33 litres. 



1 hour 76*08 „ 



COo content of air entering case 2 *80 per 10,000 



>j „ leaving „ 1 -30 „ 



Mean C0 2 content of air in contact with leaf 



during experiment 2 '05 „ 



C0 2 absorbed by leaf per hour 11 "41 c.c. 



„ per sq. metre per hour * . . 273 '2 c.c. 



