ANIMALS AND PLANTS. 167 



of the carbon, hydrogen, oxygen, nitrogen, phosphorus, 

 sulphur, and other elementary bodies contained in the 

 bean-plant, and in the seeds which it produces, are ex- 

 actly equivalent to the weights of the same elements 

 which have disappeared from the materials supplied to 

 the bean during its growth. Whence it follows that the 

 bean has taken in only the raw materials of its fabric, 

 and has manufactured them into bean stuffs. 



The bean has been able to perform this great chem- 

 ical feat by the help of its green colouring matter, or 

 chlorophyll ; for it is only the green parts of the plant 

 which, under the influence of sunlight, have the mar- 

 vellous power of decomposing carbonic acid, setting free 

 the oxygen and laying hold of the carbon which it con- 

 tains. In fact, the bean obtains two of the absolutely 

 indispensable elements of its substance from two distinct 

 sources; the watery solution, in which its roots are 

 plunged, contains nitrogen but no carbon; the air, to 

 which the leaves are exposed, contains carbon, but its 

 nitrogen is in the state of a free gas, in which condition 

 the bean can make no use of it ; * and the chlorophyll f 

 is the apparatus by which the carbon is extracted from 

 the atmospheric carbonic acid the leaves being the 

 chief laboratories in which this operation is effected. 



* I purposely assume that the air with which the bean is supplied in 

 the case stated contains no ammoniacal salts. 



f The recent researches of Pringsheim have raised a host of questions as 

 to the exact share taken by chlorophyll in the chemical operations which 

 are effected by the green parts of plants. It may be that the chlorophyll 

 is only a constant concomitant of the actual deoxidising apparatus. 

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