1902.] Influence of Carton Dioxide on Leaves, etc. 



403 



of each of the young plants was passed through a split cork fitted into 

 the central hole of the tray, and was luted air-tight with a soft mix- 

 ture of vaseline and paraffin. Two narrow tubes also passed through 

 the tray, one of which was cut short inside whilst the other extended 

 to the top of the glass covering the vessel. A slow current of moist 

 air was aspirated through each inverted beaker. In one case ordinary 

 air was used, containing from 2*8 to 3 parts of C0 2 per 10,000, whilst 

 in the other the air stream was enriched with C0 2 to the extent of 5*4 

 parts per 10,000 by passing through a small glass tower containing 

 marble, over which a regulated amount of very dilute hydrochloric 

 acid was slowly dropped. In this latter instance the air-stream was 

 passed through a wash-bottle containing a solution of sodium bicarbo- 

 nate before it entered the chamber containing the plant. In the 

 control experiment with ordinary air only water was used in the wash- 

 bottle. 



The extra carbon dioxide was only supplied during the daytime, 

 whilst during the night both chambers were supplied with ordinary air, 

 The experimental chambers were placed side by side in a well-lighted 

 greenhouse under exactly equal conditions of temperature, direct sun- 

 light being prevented from reaching the plants. 



The experiment in this instance lasted for 1 1 days, extending from 

 June 29 to July 10, 1899. 



The plants, which were almost identical in appearance, were then 

 carefully washed out of their pots, and with their roots were dried and 

 weighed. 



Dry Weight of Plants. 



A. Grown in normal air 0*856 gramme. 



B. Grown in air containing double the 



normal amount of C0 2 0*843 „ 



Experiment VI. — Another similar experiment with Vicia Fdba. 



In this case beans of as nearly an equal weight as possible were 

 germinated in pots, and a selection from the seedlings was made of 

 well-developed plants of similar appearance. 



The C0 2 was in one case increased to twelve parts per 10,000, i.e,. r 

 four times the normal amount, ordinary air being passed over the other 

 plant. The experiment lasted 10 days, from August 19th to August 

 29th, 1899. 



Dry Weight of Plants. 



A. Grown in normal air 0*872 gramme. 



B. Grown in air containing four times 



the normal amount of C0 2 0*814 „ 



The foliar area was also measured in this instance, with the following 

 result : — 



