CHYMISTRY APPLIED TO AGRICULTURE. 13 



two receivers, the one opaque, and the other transparent, 

 is convinced that germination took place in both cases at 

 the same time; but that the subsequent vegetation was 

 more rapid and vigorous under the transparent, than 

 under tYte opaque receiver. It is easy to reconcile these 

 opinions and results, though apparently so contradictory, 

 by separating the action of heat from that of light. As 

 plants transpire very little during their first stage of ger- 

 mination, if they are exposed to the united influence of 

 the two fluids, that of heat will exercise upon them its 

 full force, because there is no evaporation from them to 

 temper its effects, and their delicate organs will be with- 

 ered and dried up. It is for this reason that gardeners 

 are so careful to shelter their nurseries from the rays of 

 the sun, and not to expose their plants, till by the devel- 

 opement of their leaves they are able to moderate the 

 effiects of heat by transpiration. 



Though the action of light upon vegetation does not 

 appear to be so important as that of the other fluids of 

 which I have spoken, it is not in reality less so. Plants, 

 which are raised in the shade or in darkness, are nearly 

 or quite without color, perfume, taste, or the firmness of 

 texture of those, that are exposed to the direct rays of the 

 sun ; and if the luminous fluid does not combine with the 

 organs of plants, we cannot deny that it is a powerful 

 auxiliary in their combinations. 



It is generally acknowledged that plants do' not emit 

 oxygen gas, excepting when exposed to the direct rays of 

 the sun ; and it is known also that flowers rarely produce 

 fruit, if raised entirely in the shade. According to the 

 observations of M. Decandolle, the sensitive plant, if car- 

 ried into the shade, closes its leaves as during the night, 

 and reopens them immediately upon being again exposed 

 to the rays of the sun or of a lamp. 



The grand discoveries of Herschel have thrown great 

 light upon these delicate questions. That learned philoso- 

 pher has proved, that amongst the various rays consti- 

 tuting a pencil of light, there are some that possess nearly 

 exclusively the property of being luminous, others, that of 

 affording heat. Wollaston and Ritter have added to these 

 important facts, that there exists a third species of rays, 

 which appear to act upon bodies as powerful chymical 

 agents. 



When we reflect upon the influence which the atmo- 

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