410 



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



(3.) Nicotiana affinis. 



June 10. — Each set of plants had thrown up a flowering axis which 

 in set B (extra COo) was not quite so fully developed, but whereas 

 the flower-buds of the control plants in ordinary air had, in several 

 cases, opened normally, the buds of set B (extra COo) were much fewer 

 in number, very small, and showed no signs of opening. (See 

 Plate 6.) 



June 29. — The difference was now very striking. The plants in 

 ordinary air had flowered well, but the set B, subjected to extra CO?, 

 although possessing well-developed flowering axes, had borne no 

 flowers at all, the buds having been arrested in development. 



July 13. — There were the same well-marked differences between 

 the sets as when last noted. The plants in extra COo had now 

 thrown up several secondary axes from their base. 



(4.) Nicotiana sylvestris. 



June 10. — Set A, grown in ordinary air, were further developed than 

 those of B, and possessed larger leaves. 



June 29. — The same difference as on June 10. No flowers formed 

 on plants in extra C0 2 , whereas the controls flowered freely. 



July 13. — The same remarks apply as on June 29. 



(5.) Begonia gracilis. 



June 10. — The six plants of set A, grown in ordinary air, were 

 healthy and had flowered well. Those of set B (extra COo) appeared 

 very unhealthy, and in only one instance showed any flowers, which 

 were small, greenish, and altogether abnormal. (See Plate 7.) 



June 29. — Whilst the control plants grown in ordinary air were in 

 full flower, those of set B grown in extra COo had only a few small, 

 unopened buds, which dropped off before they opened. 



The general appearance of the plants grown in extra COo had now 

 become fairly healthy, but there was an abnormal tendency for their 

 leaves to curl downwards and inwards. 



July 13. — A very marked difference in the two sets. Whilst the 

 height was about the same the axial organs of set B, grown in extra 

 COo, were much stouter than those of the controls, whilst the inter- 

 nodes were shorter and more numerous. The plants grown in ordinary 

 air had a more spreading and less dense habit, whilst the leaves of set 

 B (extra C0 2 ) had still a marked tendency to curve downwards and 

 inwards, their colour being on the whole a darker green. 



Whilst the plants in ordinary air had flowered and fruited well, 

 those grown in extra C0 2 had either cast their buds entirely, or in 

 some few cases these had developed into small, sickly, abnormal 

 flowers, which in no case fruited. 



