406 



Dr. H. T. Brown and Mr. Y. Escombe. [Apr. 28 r 



The effect of an increased amount of CO2 in the air becomes in most 

 cases apparent within a week or 10 days from the commencement of 

 the experiment, and rapidly increases as times goes on. There is a 

 marked difference induced in the habit and general appearance of most 

 of the plants owing to a stimulation of all axial growth, accompanied 

 by a more or less pronounced shortening and thickening of the inter- 

 nodes. Usually, but not in all cases, there is an increased number of 

 the internodes, so that the height of the two contrasted sets remains 

 much about the same, but the chief difference of general habit is 

 brought about by the development throughout the plant of secondary 

 axes in the axils of the leaves, thus giving the plants grown under the 

 influence of increased COo a denser and more bushy appearance. This 

 was particularly noticeable in the Fuchsias, especially the dark-leaved 

 variety, in which every axil bore a shoot, and frequently extra axillary 

 ones. Adventitious shoots were also developed rather freely at the base 

 of the plants. 



The leaf area of the plants under the influence of increased CO2 was 

 generally found to be much reduced, not so much by the formation 

 of a less number of leaves as by the reduction in area of the indi- 

 vidual leaves. This was found to be extreme in the case of the dark- 

 leaved Fuchsias, and it was also very marked in the second crop of the 

 leaves of Lnpatiens. There was also produced in many of the plants a, 

 marked inward curling of the leaves, the extremes in this direction 

 being found in the Begonias and Fuchsias. In the dark-leaved variety 

 of Fuchsia the leaves were curled inwards like a watch-spring, which 

 would doubtless tend to reduce excessive photosynthesis by preventing 

 the normal amount of light from reaching the chloroplasts. This 

 change of habit may in fact be regarded as an attempt on the part of 

 the plant to adapt itself to its abnormal atmospheric surroundings. 



The extra CO- 2 in several cases induced a deeper green colour in the 

 leaf, and in all other parts of the plant where chlorophyll was present. 

 This was particularly noticeable in the second crop of leaves de- 

 veloped on the Impatiens, in the Begonias, and in the darker-leaved 

 Fuchsias. 



On July 19, the Sachs test for starch was applied to the leaves of 

 the two varieties of Fuchsia, Cucurbita Pepo, and Impatiens platypetala* 

 In all cases the leaves taken from the plants grown with increased 

 CO2 in the air showed a much larger accumulation of starch than did 

 the leaves of the control plants. These differences were the most 

 strongly marked in the leaves of Impatiens, which became quite black 

 with the test. 



It was, however, in the development of the reproductive organs of the 

 two sets of plants that the most striking and important differences 

 were found. Whilst the control plants in ordinary air flowered and 

 in some cases fruited luxuriantly, in the corresponding plants sub- 



