PHYSICAL PROPERTIES OF SOIL. 229 



presence in plants indicates, and yet elude our pro- 

 cesses. The possible existence of chloride of silicon 

 has been noticed. If this is not the source of the 

 chlorine of plants, it must be supposed to be evapo- 

 rated as chloride from the ocean, and consequently 

 to exist in that state dissolved in air. It is question- 

 able, whether chlorine is not accidental in plants, 

 and hence, it is not included as one of the elements 

 found in plants, or in soil (87, 89). If it is deriv- 

 ed wholly from evaporation of chlorides from sea- 

 water, then as sulphate of lime, has been detected 

 in snow and hail, it becomes a question whether 

 other inorganic salts of plants, may not have a sim- 

 ilar origin, and exist dissolved in air. 



80 



