404 



Dr. H. T. Brown and Mr. F. Escombe. [Apr. 28, 



A. Area of leaves on plant in normal air 66*9 sq. cm. 



B. „ „ in air with 



four times normal amount of CO2... 55 '6 „ 



Similar results were also obtained with young plants of Helianthus 

 annuus. 



The experiments indicate that the plants were certainly not stimu- 

 lated to increased growth by somewhat increasing the amount of C0 

 in the surrounding air. The evidence in fact points in the other 

 -direction, i.e., towards a slight diminution in the increment of dry 

 weight, and to a less development of foliar area. There were also 

 indications of certain morphological differences, which assumed some 

 importance in the light of subsequent experiments. The plants grown 

 in air slightly enriched with C0 2 had not only smaller leaves than the 

 controls, but these leaves were of a distinctly darker green, and the 

 internodes of the plants were decidedly shorter. 



The results obtained with these preliminary experiments now in- 

 duced us to extend our observations to a larger number of species, and 

 arrangements were consequently made to carry out a series of experi- 

 ments on a large scale, and under conditions which would admit of the 

 plants being kept under observation for a much longer period of time. 



For this purpose a small greenhouse adjoining the Jodrell Labora- 

 tory was kindly placed at our disposal by the Director. This was 

 divided into two compartments, each of about 380 cubic feet capacity, 

 by means of a glazed partition, which was made quite air-tight. In one 

 of these, compartment A, the experimental plants were grown in 

 normal air, whilst the air of compartment B could be enriched to any 

 desired extent with carbon dioxide supplied from a receiver of the 

 liquefied gas placed in an adjoining building. The gas before entering 

 the greenhouse was bubbled through a wash-bottle at a rate which 

 previous experiments had shown to be necessary in order to keep the 

 composition of the air approximately constant. Frequent analyses of 

 the air in both compartments were made as a check. 



The current of carbon dioxide was started each day at 6 a.m., and 

 continued until 6 p.m., both greenhouses being closed during the day, 

 and the glass top and sides of the houses were white-washed over in 

 order to exclude direct sunlight, whilst at the same time allowing 

 plenty of illumination. During the night both greenhouses were 

 opened and well ventilated from the outside, so that for 12 hours 

 out of the 24 the atmospheric conditions were identical. Care 

 was taken to maintain the temperature, degree of illumination, 

 and the hygroscopic state of the two compartments as nearly as 

 possible identical, the only point of difference being in the composition 

 of the air.* 



* The plants were grown in a rich garden soil containing all the mineral and 

 nitrogenous constituents necessary for luxuriant growth. 



