ABSORPTION OF SALTS. 63 



The section of the roots, even their destruction, favors, as we 

 ^ave already said, the introduction of the matters dissolved. Plants 

 whose roots had been removed, no longer selected the substances 

 dissolvsd in so striking a manner as they did previously ; after muti- 

 latiort they absorbed them almost indifferently, in larger doses, and 

 perceptibly in the same proportion as the water which held them 

 in solution. 



Roots with their spongioles entire, therefore, suffer one substance 

 in solution to penetrate the plant in preference to another. The 

 chlorides of potassium and of sodium, for instance, find entrance 

 more readily than the acetate and nitrate of lime : sugar more readily 

 than gum ; and precisely as when isolated, are these substances, 

 when combined, absorbed in much less proportion than the menstruum 

 or water of solution. 



M. de Saussure is not disposed to admit that the preference which 

 plants evince for certain salts, for certain dissolved substances, results 

 from any particular faculty, from any special affinity. He rather 

 inclines to believe that it should be attributed to the degree of 

 fluidity, or of viscidity communicated to the water by the different 

 substances dissolved ; thus the acetate and nitrate of lime, with the 

 same proportion of liquid, form more viscid solutions, which pass 

 with more difficulty through a filter, than the alkaline sulphates and 

 chlorides ; and these latter salts in solution were absorbed by vege- 

 tables in greater abundance than the calcareous salts. Gum, which 

 imparts more viscidity to water than sugar, is also less capable of 

 being absorbed. Finally, pure water, more fluid than any of the 

 solutions tried, was also that which vegetables preferred to any 

 other. 



In the results of the incinerations which we have mentioned, it is 

 obvious that in many plants salts are met vt^ith in very small propor- 

 tion. This circumstance has induced several physiologists to con- 

 sider the mineral substances found in vegetables as purely accidental, 

 and consequently unnecessary to their existence. M. de Saussure, 

 however, observes that this scantiness is no true indication of their 

 inutility, and he mentions that the phosphate of lime, which forms 

 an element in the organization of an animal, does not probably 

 amount to one five-hundredth part of the entire mass. We shall add, 

 that as the phosphate of lime was met with by M. de Saussure in 

 the ashes of all vegetables which he examined, and as all the analyses 

 performed since the original labors of this celebrated chemist have 

 tended to confirm the accuracy of his general conclusions, we have 

 no ground for supposing that plants could exist without the interven- 

 tion of saline matter. There are annual plants which, when burned, 

 leave more than 10 per cent, of residue ; and vegetables cultivated 

 in soils free from saline or alkaline matter, and watered with dis- 

 tilled water, though they will live and ripen their seeds in some 

 instances, still they never acquire the vigor which they possess when 

 grown in a fertile soil. 



Duhamel ascertained that marine plants languish in soils destitute 

 of chloride of sodium ; and this is so much the more readily oon- 



