1902.] 



Influence of Carbon Dioxide on Leaves, etc. 



405 



Two series of experiments were made, one in the summer of 1900, 

 .and the other in the summer of 1901. 



The composition of the air as regards carbon dioxide differed very 

 much in these two experiments, in one case the air being enriched with 

 about 5*5 to 6 per cent, of the gas, i.e., 180 to 200 times the normal 

 amount, whilst in the other case the mean CO2 content was only 0*114 

 j)er cent, i.e., between three and four times the normal amount. 



Contrary to what might have been expected, the general results, 

 compared with those obtained with the control plants in ordinary air, 

 were practically identical in the two sets of experiments, notwith- 

 standing the large range of something like 1 to 50 in the C0 2 content 

 of the enriched air. 



Since the greater interest attaches to the experiments with the 

 smaller increment of C0 2 , we shall confine our attention almost entirely 

 -to this set in the remarks which follow. 



The plants taken for this experiment were as follows : — 



(1.) 8 plants of Cucurbita Pepo (Italian Gourd). 



(2.) 8 „ Impatiens platypetala. 



(3.) 6 „ „ Nicotiana affinis. 



(4.) 6 „ „ Nicotiana sylvestris. 



(5.) 10 Begonia gracilis. 



(6.) 6 ,, Solanum atropurpureum. 



(7.) 12 ,, j, Kalanchoe Welwitscliii. 



(8.) 6 „ Fuchsia, var. with light coloured leaves. 



(9.) 6 ,, „ Fuchsia, var. with darker leaves. 



One-half of each set was placed in compartment A, the other half in 

 compartment B, the plants being carefully matched as regards size and 

 general appearance, and arranged symmetrically as regards the glass 

 division separating the two compartments, 



Set A in ordinary air (controls). 



Set B in air enriched with CO2. 



The experiment was commenced on May 13, and continued until 

 July 29, i.e., for a period of 77 days. 



The mean content of the air in C0 2 during the daytime was : — 



In compartment A, 3*29 parts per 10,000. 

 ■>■> ?) -Bj 11 47 ,, 



:8o that the atmosphere of compartment B contained during the day- 

 time about three and a-half times more C0 2 than that of compart- 

 ment A. 



A careful record was made of the differences in appearance of the two 

 sets of plants on June 10, June 29, and July 13, that is to say, at 28, 

 47, and 61 days from the commencement of the experiment. The 

 results are given in detail in the Appendix to this paper, and may be 

 summarised as follows : — 



