ASSIMILATION. 109 



into gases before it is eliminated, but only a part of it ; the ' 

 rest appears under the form of those solid an:d liquid faeces 

 excreted from the system by the appropriate organs, and 

 its final decomposition takes place when it is separated from 

 the organism, just as the leaf is resolved into its original 

 elements after it is detached from the branch. We cannot 

 see any difference except in the greater degree of its 

 simplicity, between this process in the plant and in the 

 animal. The dead matter in the interior of the organism 

 is of service, since it strengthens the fabric of the plant, 

 and therefore no provision has been made for effecting its 

 removal. It cannot be called waste matter. It, is other- 

 wise with the foliage and flowers with which plants are' 

 annually adorned. These cease to be of any further ser- 

 vice as soon as they are dead ; they are therefore separated 

 from the plant as waste matter. 



We have seen that plants subsist on the food which they 

 find in the earth and atmosphere, in a condition suitable 

 for absorption into their organism; that animals, on the 

 contrary, have to use organs for the. prehension and the 

 preparation of their food before it can be absorbed. There 

 is the same simplicity in plants, and additional complexity 

 in animals, in the elimination of their waste matter ; it is 

 thrown off at once from the'plant, but in animals, a special \ 

 system of organs has been superadded to the general organ- 

 ism, in order to effect its removal. 



ASSIMILATION IN PLANTS AND ANIMALS. 



The food of plants is digested and rendered nutritive 



in their leaves ; that of' animals is prepared for circulation 



in their stomach. The leaves have been called the lungs 



of plants, and the process of respiration has been repre- 



10 



