412 Influence of Carbon Dioxide on Leaves, etc. [Apr. 28, 



July 13. — In no single case had a bud opened on the plants grown 

 in air containing increased amounts of C0 2 , and their denser habit was 

 still more strongly marked. The leaves were also smaller, of darker 

 green and with a tendency to curl up, whilst the internodes were a 

 little stouter, and shorter, and the colour of the axes was a little more 

 pink. 



(9.) Fuchsia. — (b) Darker-leaved Variety. 



June 10. — There was already a marked difference between the two 

 sets as regards general habit and appearance. The control plants in 

 normal air possessed long and slender axes and were freely developing 

 flower-buds. Set B, grown with extra C0 2 , had a very abnormal 

 appearance; their main axes were much shorter, whilst the leaves 

 were extremely small and curled inwards ; there was also a great 

 development of axillary shoots, and adventitious ones at the base of 

 the stems. (See Plate 9.) 



June 29. — The above difference had become still more accentuated. 

 No flowers had been formed on set B, grown with extra C0 2 in the 

 air. 



July 13. — The differences between the two sets were now extreme. 

 The plants of set B (extra C0 2 ) had a most abnormal appearance. 

 Their leaves were all extremely small, of a much darker green, and 

 were rolled up in an inward spiral like that of a watch-spring. There 

 was also a profuse development of secondary axes in the axils of most 

 of the leaves, from the base of the primary axis up to its apex. This 

 habit of growth gave the whole plant a much denser appearance than 

 that of the control plants grown in ordinary air. The internodes were 

 on the whole shorter and stouter than those of the controls, and differed 

 markedly in colour : whereas those of the controls had the ordinary 

 blood-red appearance, the internodes of the plants grown in extra C0 2 

 were pinkish-green. No flowers had developed on the plants of set B, 

 grown in extra C0 2 . (See Plate 10.) 



DESCRIPTION OF THE PLATES. 



Plate 5. — Impatiens platypetala. 



Under experiment for 28 days. 



A. Plants grown in ordinary air. 



B. in air containing 11*4 parts per 10,000 of C0 2 . 

 Plate 6. — Nicotiana affinis. 



Under experiment for 28 days. 

 A . Plants grown in ordinary air. 



P>. „ in air containing 11*4 parts of C0 2 per 10,000. 



Plate 7. — Begonia gracilis. 



Under experiment for 28 days. 



A. Plants grown in ordinary air. 



B. „ in air containing 11 *4 parts of C0 2 per 10,000. 



