CH. IV.] THE LEAVES. 149 



rience, for his blanched sea-kale, endive, and lettuce 

 are totally dissimilar in flavour and appearance to 

 the plant left in its natui'al state. 



Sir H. Daxj excluded a cos-lettuce from the light. 

 In six days it was rendered very pale, and, at the 

 end of another week, it was quite white : the growth 

 of the plant was checked, and the analysis of its 

 leaves shewed that they contained more carbonic 

 acid and water, but less hydrogen and residual 

 cai'bon, than an equal weight of green leaves. 



It deseiTes notice, that it has been proved by the 

 experiments of Dr. Hope and others, that light from 

 artificial sources may be concentrated so as to 

 enable plants to absorb oxygen and perfect those 

 elaborations on which their green colour depends ; 

 and the light of the moon has a similar influence. 

 A similar concentrated light will make the pim- 

 pernel and other flowers which close until sun-rise 

 open their petals, and rouse from their rest ; a fact 

 which gives another reason why plants in rooms 

 frequented at night become weak and exhausted 

 sooner than those that remain, as nature dictates, 

 unexcited at night. 



The yellow, red, and light brown tints wliich 

 render the fohage of our plants so beautiful in 

 autumn, arise from the absorption of an excess of 

 oxygen gas. When the reduced temperature of the 

 season deprives a leaf of the power to elaborate the 



