OBSERVATIONS ON LEAVES. 43 



(which gas is composed of carbon and oxygen,) this gas will 

 be absorbed, but the carbon will be retained to increase the 

 growth of the plant, while the oxygen gas will be returned, 

 and thus that portion of the air which was converted into 

 carbonic acid during the night, will be re-converted into oxy- 

 gen gas again during the day. 



These surprising changes, which are performed by the vi- 

 tal powers of the plant, or during its growing state, are sup- 

 posed to be the means, at least in part, by which plants in- 

 crease ; for by other experiments it has been found, that 

 when any growing vegetable is confined in a portion of car- 

 bonic acid made by art, the carbon is absorbed and retained, 

 while the oxygen is returned. 



Now it is also known by experiments that the atmosphere 

 always contains a portion of carbonic acid gas, and that the 

 solid part of vegetables growing in the open air, is chiefly 

 carbon. From these facts it is inferred that the increase, or 

 growth of plants, depends much on the carbon which they ab- 

 sorb from the atmosphere, in the form of carbonic acid, the 

 oxygen being emitted, while the carbon is retained. 



If there is too great an accumulation of oxygen, as when 

 a plant is kept in a dark place, then it will grow towards the 

 nearest ray of light, which if it does not reach, it will re- 

 main white, or etiolated, and sickly. In this state, as when 

 a potato shoots out its stem in a cellar, plants contain little 

 carbon, being chiefly composed of water and sap, but as soon 

 as they gain the influence of the sun, they begin to part with 

 oxygen, increase their quantity of carbon, and assume a green 

 and healthy aspect. These circumstances seem to explain 

 the reason why many kinds of fruit, when gathered green 

 and laid in the sun, soon part with their harsh sour taste, and 

 become mild, sweet and agreeable, or, in other words, ripen. 

 By the influence of the light, their superabundance of oxy- 

 gen on which their acerb taste depended, is expelled, and at 

 the same time the carbonaceous matter and the essential oil, 

 on which their agreeable flavor depends, are increased. That 

 these changes are produced by the influence of light, and not 

 by the heat of the sun alone, is proved by the well known 



When does a plant convert carbonic acid into oxygen ? In what man- 

 ner are the solid parts of vegetables accumulated ? Why do plants grow- 

 ing in the dark remain white and sickly ? In what respect is the composi- 

 tion of such plants deficient ? Why do green fruits laid in the sun be- 

 come sweet and pleasant to the taste ? 



