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FACTS AND FANCIES. 



means of microscopic pores guarded by cun- 

 ningly-contrived valves opening or closing 

 according to the hygrometric state of the air ; 

 connected with the stem of the plant by a 

 system of tubes strengthened with spiral fibres 

 within, — the structure of the leaf is, mechan- 

 ically considered, of extreme beauty and com- 

 plexity. But its living functions are still more 

 wonderful. Receiving the water from the soil 

 with such materials as it brings thence in solu- 

 tion, and absorbing carbonic dioxide and am- 

 monia from the air, the living protoplasm of 

 tjie leaf-cells has the power of chemically chang- 

 ing all these substances, and of producing from 

 them those complicated and otherwise inimita- 

 ble organic compounds of which the tissues of 

 the plant are built up. The force by which 

 this is done is that of the solar heat and light, 

 both admitted freely into the interior of the 

 leaf through the transparent epidermis, and 

 therein imprisoned, so as to constitute a pow- 

 erful storehouse of evaporation and chemical 

 energy. In this way all the materials available 

 for the maintenance of life, whether vegetable 

 or animal, are produced, and no other structure 

 than the living vegetable cell, as it exists in 

 the leaf, has the power to effect these miracles 



