NUTRITION. 47 



imbibing it. Plants being utterly without loco- 

 motion, and unable to seek their own food, it 

 follows that their nourishment must be so abun- 

 dant in nature as to be almost universally within 

 reach, and so easy of absorption as to offer no 

 resistance to their comparatively feeble powers 

 of action. These necessary conditions are beau- 

 tifully fulfilled by the spongioles and by the 

 nature of water. The spongioles make no selec- 

 tion of healthy material for the nourishment of 

 the plant : and the absorption of fluid through 

 their medium appears to be regulated merely by 

 the readiness with which certain solid substances 

 held in solution can be received along with the 

 water. Thus the action of the spongioles sepa- 

 rates a portion of the water from a solution of 

 gum arabic, leaving the gum behind in the re- 

 maining solution, in an increased state of satu- 

 ration ; but sulphate of copper in solution one 

 of the substances most injurious to vegetation 

 is rapidly absorbed. Dr. Carpenter, however, 

 mentions an exception to this, in the power which 

 some plants exert of taking up certain mineral 

 substances which seem peculiarly requisite for 

 them. He says, " if a grain of wheat and a pea 

 be grown in the same soil, the former will obtain 

 for itself all the silex, or flinty matter, which the 



