8 



Fagus^ and the common kinds of Finns. While leaves of Acer show 7 

 to 9 per cent of ash and those of Salijc 4 to 6 per cent, the leaves of 

 Finns montana and F. austriaca show only 0.58 per cent and 0.74 per 

 cent, respectively (Ebermayer). There is more ash in the leaves than 

 in the roots or stems, more in the roots and stems than in the seeds, 

 and more in the seeds than in the wood. 



ECOLOGICAL AND PHYSIOLOGrlCAL ROLE OF MINERAL SUBSTANCES. 



A question of fundamental importance is whether a certain mineral 

 constituent has one or several functions to perform, and in the latter 

 case whether at least one of these several functions may not be per- 

 formed by some other related constituent — in other words, whether a 

 partial substitution in the organisms would be possible. When a mere 

 neutralization of acids or an osmotic action is involved there can be no 

 doubt that potassa or lime may be replaced by soda, or when incrus- 

 tation of a tissue is necessary for protection the place of calcium car- 

 bonate might be taken even by silica. The solution of various mineral 

 salts produces osmotic pressure and motion required also by animals. 

 Thus beef tea containing 0.35 gram of salts per liter, exerts an osmotic 

 energy of several atmospheres, of which, however, only about one-fourth 

 can be realized in the stomach, since the blood itself also contains min- 

 eral salts. However, it suffices to produce an aqueous current from the 

 blood to the stomach, while in the intestines the current takes the oppo- 

 site direction.^ Such functions are not specific, however. But in the 

 purely physiological functions of a chemical nature not even a partial 

 substitution is possible, notwithstanding that various assertions have 

 been made to the contrary. The most novel supposition in connection 

 with this idea of substitution, and one very amusing to chemists, is 

 that seriously made in a recent text-book of plant i^hysiology, that is, 

 that on other planets there may exist living organisms in Avhich the 

 carbon of the organic matter is replaced by silicon. 



In order to furnish a foundation upon which to base a theory of the 

 special functions of the various mineral constituents, separate analyses 

 for each kiud of organ are indispensable. In former times entire 

 plants or animals were subjected to incineration and the ash analyzed, 

 but such results were of very restricted value.- A distinction may be 

 drawn between ecological ,and i)hysiological functions. In the former 

 case the mineral compound serves either as a mechanical support of the 

 organic forms, as does for example the calcium phosphate in the case 

 of bones, and probably the silica in grasses, feathers,-^ and hair; or it 

 furnishes a protection against noxious inliuences from the outside, and 

 against the attacks of enemies,^ as do the needle crystals of calcium 



1 Koppe, Therap. Monatshefte, 1897. 



-Thus one author has iuferred from his analyses that there is less magnesia in cats 

 and dogs and less i)ota8sa in dogs than in rabbits (Zeitschr. Biol., Vol. X, p. 321). 



^The organic silica compound in feathers was recently studied by Drechsel. 



■•Tt has been asserted that the siliceous deposit in the bark of Fagus and Acer and 

 in the leaves of various other plants forms a i)rotection against parasitic fungi. 



