92 AK ATOMY AND PHYSIOLOGY OF 



re-dissolye these crystals. It is true tliat nutritive substances (starch, 

 fixed oils, &c.) are frequently produced in greater abundance than the 

 i^equirements of the moment demand, and are deposited in the cells of 

 particular organs, but these deposits are only temporary accumulations of 

 food to be made use of subsequeiitly; those deposits of insoluble salts 

 appear much more likely to be intended to remove from the circuit of 

 active juices, compoundb which are superfluous to the plant. 



Again, this theory does not explain the exchange of different bases 

 at different periods of the age of the same organ. From the analyses 

 of Saussure was deiived the general rule, that young organs are espe- 

 cially rich in soluble alkaline salts, older plants in earthy salts and 

 metals. 



A second doctrine propoimded by Liebig, is connected most closely 

 with this opinion as to the office of the alkalies to neutralize the organic 

 acids, namely, the notion that for every species of plant, the amount of 

 oxygen of the carbonic acid contained in its ash, in the combustion of 

 salts originating from vegetable acids, is constant, xio matter what soil 

 the plant may grow upon (^^AgricuU, Chem,'' Qth ed ). For Liebig assumes 

 that a plant forms no more of the acids which it produces, than is 

 directly requisite for its vital operations, and that these thei'efore take 

 just so much alkali as will fix these determinate quantities of acid. But 

 weighty objection's may be opposed to this doctrine. I have already ob- 

 served that many plant*^ do not produce the organic acids in that quan- 

 tity which they would require were these converted into neutral com- 

 pounds, but in very coubiderable &U2)erabundance, as for example, all 

 specimens of Gaotus unceasingly deposit extraordinarily large masses of 

 tartrate or oxalate of lime in their cells, as insoluble crystals; the oxalic 

 acid of these crystals is wholly withdrawn from the nutrient operations, 

 yet elementary analysis would make its lime appear to exist in the state 

 of carbonate, while at the same time, no conclusion could be drawn from 

 its quantity, as to the amount of acid neces'^ary in the nutrient processes 

 of these plants. Moreover, all the alkalies which appear in the ash as 

 carbonic salts, are not combined with organic acid in the living plant, 

 but in many plants crystals of carbonate of lime occur ; carbonic salts are 

 deposited in the sxibstance of many cell-membranes, and all cell-mem~ 

 branes are combined with alkalies and eaiiihs ; consequently, we cannot 

 draw from the analysis of ashes, as Liebig assumed, a proof of that law, 

 and this is the less possible since, moreover, the fixed alkalies may be 

 replaced by ammonia. 



Whatever may be the character of the chemical action to which 

 neutral compounds ovt^e their origin, it is at all events, beyond 

 doubt that they are produced by a deoxidizing process taking 

 place under the influence of light. The effect of the deoxidation 

 extends still further, for there can scarcely be a plant which does 

 not contain compounds in which the oxygen is not contained in 

 smaller quantity, in proportion to hydrogen, than in water, even 

 if it be not altogether wanting. To this class belong chlorophyll 

 and the wax connected with it, the incrusting substances of the 

 wood-cells, the fixed and essential oils, resin^ caoutchouc, &:c. 

 "With the exception of the fixed oils, wMch doubtless originate 



