CHAPTER V. 



ON THE SOLID EARTHY SUBSTANCES WHICH ARE 

 ASSIMILATED BY PLANTS. 



The solid earthy matters, such as potash, 

 soda, magnesia, lime, silex, phosphorus, all of 

 which perform important oflSces in the growth 

 jof plants, are next to be considered ; and here 

 it must be observed that these substances differ 

 materially from the gases already discussed. 

 In this latter case it has been seen how the 

 gaseous bodies exist as solids, as liquids, and 

 as gases, in each state performing important 

 functions in the vegetable economy; but, in 

 noticing the earthy salts, it must be distinctly 

 understood that they exist only as solids, and 

 that the soil exclusively contains them. Hence, 

 the only way in which they can be absorbed 

 into the plant is, by the spongelets of the roots 

 when in a state of solutioti.* 



The analysis of a few vegetable structures is 



* This iact as a general rule is perfectly true ; but the at- 

 inoq>here over the sea contains a very small portion of the 

 saline matter of the ocean in sc^ution, which may serve to ac- 

 count for the circumstance that all (dants growing on or near 

 the sea-shore, assimilate soda in their structure. 



