114 Observations on Liehig^s " Organic Chemistry" 



continues, are requisite for the formation of organs destined for 

 special functions peculiar to each family of plants; these are 

 found in the ashes of incineration, though in a changed state. 

 All substances in solution in a soil are absorbed as a sponge 

 absorbs liquid, without selection he says, those that are wanted 

 retained, and the rest rejected as excrement. Phosphate of 

 magnesia is an invariable constituent of all the seeds of grasses, 

 is contained in the outer horny husk of grain, and introduced 

 into the bread and beer : it is contained in the greatest quantity 

 in bran, and forms often large crystalline concretions in the 

 coQCum of millers' horses ; and, when ainmonia is mixed with 

 beer, separates as a white precipitate. Most plants, perhaps all, 

 he continues, contain organic acids in combination with bases of 

 potash, soda, lime, magnesia, &c. These bases diminish in 

 fruits, as the acids diminish in ripening; and the quantity is 

 greater in those organs which prepare the food, as in leaves, 

 compared with those where it is assimilated, as in the mass of 

 woody fibre. The potato contains more before blossoming than 

 after it. The fu marie and oxalic acids in liverwort, the roc- 

 cellic acid in the Roccella tinctoria, the tartaric acid in vines, and 

 other peculiar acids formed in peculiar plants, show that they 

 are essential to them. All yield by incineration carbonic acid 

 united to a base, all therefore must contain, he says, salts of 

 orgajiic acids ; and, as we know the capacity of saturation of 

 acids to be unchanging, hence, on whatever soils plants grow 

 naturally, they must contain an invariable quantity of alkalies, 

 culture alone will cause deviation. The absence of one alkali, 

 he says, is compensated for by another similar in its mode of 

 action ; and he shows by analysis, by De Saussure and Berthier, 

 of the ashes of the pine tree from different soils, that, though the 

 quantities of potash, lime, and magnesia varied, yet the quan- 

 tities of oxygen contained in the amoimt of the three bases were 

 the same in each ; if the magnesia or lime were less, it was made 

 up in the greater quantity of potash or soda. When there was 

 any variation in the quantities, it was found that the bases were in 

 combination with inorganic acids, as the sulphuric, phosphoric, 

 &c. These remarkable approximations, he says, cannot be 

 accidental, and, if further analysis confirm them, must show 

 that the bases and acids are always proportional. It is not 

 known, he says, in what form silica, manganese, and oxide of 

 iron are contained in plants ; but we are certain that potash, 

 soda, and magnesia can be extracted from all parts of their 

 structure in the form of organic acid salts; and lime, unless 

 when present as insoluble oxalate of lime, as in lichens, and 

 there supplying the place of woody fibre. Even double acid 

 salts, as the tartaric and oxalic (which acts like a double acid), 

 have only one base, and are never quadruple; the capacity of 



