Dr Alison on the Principle of Vital Affinity. 145 



it is to be found in the plant. A fir-tree, the ashes of which 

 were analysed by a most accurate chemist, grew in Norway, 

 on a soil to which common salt was conveyed in great quanti- 

 ty by rain-water. How did it happen that its ashes contained 

 no appreciable quantity of salt, although we are certain that 

 its roots must have absorbed it after every shower? We 

 can explain this only by the observations above referred to, 

 which have shewn that plants return to the soil all substances 

 unnecessary to their own existence ; and we are thus led to 

 the conclusion that the alkaline bases, existing in the ashes 

 of plants, must be necessary to their growth, since, if this 

 were not the case, they would not be retained." (lb. p., 103, 4.) 

 Another inference is at least equally obvious, that plants have 

 the power of fixing and retaining within them those matters 

 which are suited or essential to their composition ; and this 

 power we regard as the simplest form of vital affinity. It may 

 be said, that the alkaline bases are thus fixed in plants, because 

 they enter into combination with organic acids, and that, 

 therefore, it is the formation of these acids, not the retention 

 of the bases which combine with them, that is truly the vital 

 change. But this does not apply to other saline matters con- 

 tained in vegetables, which must have been taken up from the 

 soil in the same state in which they are found in the plants, 

 e. g., the phosphate of magnesia, which is " an invariable in- 

 gredient in the seeds of grasses ;" or the silica which is found . 

 in certain parts of various plants. 



Were it not for this selecting and appropriating power, 

 indicating a simple attraction of some parts of the vegetable 

 for certain earthy or saline matters only, we should find some 

 salts of alumina, as well as of lime or magnesia, in the ashes 

 of almost all vegetables, — that earth existing in large quan- 

 tity in all fertile soils, whereas it is " very rarely found in^ 

 the ashes of plants.'' "^ ' • 



In the animal kindom the same power of simple selection 

 and extraction is more fully exemplified, perhaps most strik- 

 ingly in the development of many of the lower classes, of 

 which the organization is simple, and the matters deposited 

 from the nourishing fluid remarkably diversified, as in many 

 of the radiata and mollusca, which have horny and earthy 



VOL. XLI. NO. LXXXI. — JULY 1846. K 



