ON PLANTS. 101 



their color, they absorb oxygen during the night, but lose 

 the power of giving it out during the day : hence he in- 

 ferred, that the accumulation of oxygen destroyed the 

 green color and produced the various tints which the au- 

 tumnal leaf assumes. 



Emily. We know the power that oxygen has in chang- 

 ing the colors of metals : it is not therefore, surprising 

 that it should produce effects somewhat similar on plants ; 

 but if it is oxygen which gives rise to the red and yellow 

 color of dying leaves, may it not also be the cause of the 

 various hues of living flowers ? Mr. Macaire should 

 have prosecuted his researches to have discovered this. 



Mrs. B. He did so ; and was led by their result to 

 think, that it is to the various quantities and modes of 

 combination of oxygen, that the different colors of flowers 

 is to be attributed. 



The third mode by which light acts on plants, is by fa- 

 cilitating, and consequently increasing, their absorbent 

 powers. The more the cause is augmented, the more the 

 effect is increased. Tell me now, what do you suppose 

 would be the result of great intensity of light ? 



Emily. To be enabled to answer your question, it would 

 be necessary to be acquainted with the plants of tropical 

 climates, where light as well as heat is so much stronger 

 than in our latitudes. 



Caroline. It would be more easy, in this mountainous 

 country, to study the plants which grow on their summits, 

 where they are so much more exposed to light than in the 

 valleys or the plain ; and I recollect observing, that they 

 are generally of a deeper green, which is no doubt owing 

 to the greater deposition of carbon. 



Emily. I have remarked, also, how much deeper the 

 green color of vegetation is in Italy than in England. 



Mrs. B. In the tropical climates this difference is still 

 more remarkable. But what is very extraordinary, M. 



560. What causes leaves in autumn to assume a red or yellowish 

 color! 561. What fact is mentioned by Emily which renders Mr. 

 Macaire's opinion on the color of plants probable! 562. What fur. 

 ther did he suppose in relation to the color of plants'? 563, What is 

 the third mode in which light operates on plants! 564. What ques- 

 tion is asked by Mrs. B. as to the effect of light on plants'? 565.' 

 In reply what does Caroline say she has observed! 566. And what 

 has Emily remarked in relation to the same subject! 567. Where 

 does Mrs, B. say this difference is more apparent! 



