6 THE ACTION OF LIGHT UPON PLANTS. 



the assimilation of carbon and the evolution of oxygen 

 result 



" He had satisfied himself that in fine weather a 

 plant consisting chiefly of leaves and stem will, if 

 confined in the same portion of air night and day, and 

 duly supplied with carbonic acid during the sunshine, 

 go on adding to the pro])ortion of oxygen present, so 

 long as it continues healthy, at least up to a certain 

 point 



'• Considering the quantity of oxygen generated by 

 a very small portion of a tree or shrub introduced, he 

 saw no reasons to doubt that the influence of the 

 vegetcdjle might serve as a complete compensation for 

 that of the animal hingdomr 



In 1837, Mr. Ward made a Eeport to the British 

 Association, " On the Growth of Plants in closed 

 Cases," at the end of which he " directed the atten- 

 tion of the members to the development of animal 

 life upon the same principles." He was " quite certain 

 that a great number of animals would live and thrive 

 under this treatment." 



In his treatise on the same subject, published in 

 1842, he dilates a little on this matter, chiefly with 

 regard to increasing the purity of air for breathing in 

 large towns, as a remedy for disease. " The difficulty 

 to be overcome," he observes, "would be the removal 

 or neutralization of the carbonic acid given out by 

 animals ; but this in the present state of science 

 could easily be effected, either by ventilators or by 

 the growth of plants in connexion with the air of the 

 room, so that the animal and vegetable respirations 

 Qnight counterbalance each other. The volume of the 



