216 Messrs. Gladstone on the Growth of Plants in various Gases, 



as the source whence it is obtained ; but when the minuteness 

 of the quantity is taken into account, the assimilation of nitrogen 

 by plants, though improbable, may certainly still be held an 

 open question. 



It is to the decomposition of the carbonic acid in the atmo- 

 sphere that vegetables are mainly indebted for the carbon which 

 forms the basis of their structure. The proportion of carbonic 

 acid in the air in which different plants will thrive has engaged 

 the attention of many experimenters, and is still the subject of 

 investigation. This at least is clearly ascertained, that, unless 

 in strong sunshine, plants are destroyed by being placed in an 

 atmosphere of pure carbonic acid. 



The aqueous vapour in the air not only supplies hydrogen and 

 oxygen to the organized vegetable structure, but serves many 

 other purposes of a more physiological character. 



We proposed examining the growth of plants when exposed to 

 the action of gases that do not occur in the normal atmosphere, 

 or of the ordinary gases in very unusual proportions. 



Our first experiment was made with hydrogen gas. A pansy 

 was placed in an atmosphere consisting of 95 per cent, of hy- 

 drogen and 5 per cent, of carbonic acid. The glass vessel in 

 which it was confined had a capacity of 53 cubic inches. It 

 was inverted over water, so that connexion with the outer air 

 was entirely precluded, and yet there was very little surface of 

 water exposed to the artificial atmosphere within. A little ad- 

 ditional carbonic acid was introduced from time to time to re- 

 place that absorbed by the liquid. The plant when first experi- 

 mented upon had one blue flower in full bloom and one in the 

 bud ; for the first ten days the bud was gradually opening ; but 

 a slight mouldiness then came on, which increased during the 

 next fortnight, by which time the plant having drooped deci- 

 dedly, it was thought unnecessary to prolong the experiment. 

 For the sake of comparison another pansy was placed in a glass 

 vessel filled with atmospheric air, all other circumstances being 

 equal ; the plant became mouldy at about the same period as the 

 other ; but the mould did not advance beyond the lower leaves, 

 and the plant continued healthy for weeks. 



Two flowering grass-plants {Poa annua) were placed in vessels 

 of the same character and capacity as in the preceding experi- 

 ment, and protected from the external air in the same manner. 

 The one vessel was filled with pure hydrogen gas, the other with 

 common air. The plants grew and appeared healthy for about 

 a fortnight, when mouldiness supervened in each instance. Thus 

 the substitution of unmixed hydrogen gas for the normal atmo- 

 sphere produced no visible alteration. 



The next experiment was with a mixture of hydrogen and 



