1 82 MODERN IDEAS OF EVOLUTION 



either by certain low-browed and unintelligent batra- 

 chians or by their Maker. 



2. Nature presents to us very remarkable co- 



Aopcrations of dissimilar and widely separated matters 

 and forces. I have referred to the numerical arrange 

 ments of the leaves of plants ; but the leaf itself, in 

 its structure and functions, is one of the most remark 

 able things in nature. Composed of layers of loosely- 

 placed living cells, with air-spaces between them ; 

 / enclosed above and below with a transparent epi- 



^dermis, the spaces between the cells communicating 

 with the atmosphere without, by means of micro 

 scopic pores, guarded by cunningly 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 or 

 thickening of their walls within the structure of the 

 leaf is, mechanically considered, of extreme beauty 



^ and complexity. 



But its living functions are still more wonderful. 

 ^Receiving the water from the soil with such materials 

 as it brings thence in solution, and absorbing carbonic 

 H dioxide and ammonia from the air, the living proto 

 plasm of the leaf-cells has the power of chemically 

 changing all these substances, and of producing from 

 them those complicated and otherwise inimitable 

 ^organic compounds, of which the tissues of the plant 

 are built up, and which they also prepare for other 

 tpurposes in the plant. The force by which this is 



