AS ILLUSTKATED BY THE POTATO MUEKAIN. 185 



that we may well suppose that all inward diseases of plants 

 actually derive their origin from an abnormal condition of this 

 coat, and inasmuch as the peculiar power of the chemical pro- 

 cess in the cells is apparently concentrated there, its depravation 

 first calls into existence the symptoms of disease which are per- 

 ceptible at a later period in the other portions of the cells. 



I subscribe, indeed, to the doctrine first put forth by Saussure 

 and Davy, and at a later period extended by Boussingaidt and 

 Liebig, which lays so great stress on the inorganic substances in 

 plants. I believe, as Liebig first expressed it, that the whole 

 multiplicity in the vegetable kingdom, as far as it rests and de- 

 pends on a chemical process, arises in the first instance exclu- 

 sively from the action of the difierent qualitative and quantitative 

 combinations of the inorganic substances which the plant re- 

 ceives from the earth, and that consequently its meagre or 

 luxuriant growth, its healthy or diseased condition, must be de- 

 rived from these substances. It appears to me, for instance, to 

 be clearly established by the investigations of Boussingault and 

 Liebig, that the formation of the organic substances of the 

 Dextrin and Protein Category is entirely dependent on the pre- 

 sence of certain inorganic matters, without which the greatest 

 superfluity of organic elements in the available combinations 

 is utterly useless to the plant. Although it is indubitable that 

 the formation of Proteinous matters depends on the presence of 

 phosphorated salts, that of matters of the Dextrin group, on the 

 contrary, of non-phosphorated alkaline salts, tlie following inves- 

 tigation will render the subject even more probable. 



The proportional rarity of phosphates in most geological for- 

 mations, and also in the soils which are wholly or principally 

 formed from them, is Avell known ; on the contrary, they are ac- 

 cumulated in soils principally formed of decomposed vegetable 

 matter after being slowly collected by the plants. Animal ex- 

 crements are very rich in these salts, and therefore manured 

 fields, and especially gardens, contain a greater proportion than is 

 normally present in plants, or can be consumed by them. But 

 the influence which inorganic substances in the soil exercise on 

 vegetation depends upon their being generally present. For since 

 plants have not the power of choosing their own nutriment, and 

 since the proportions in which soluble substances present them- 

 selves for absorption can be altered by endosmose within very 

 narrow limits, it is equally important that the substances which 

 are requisite for plants should be contained in the soil in some- 

 thing like the projx^r proportions, since the plants are otherwise 

 compelle<l to receive matters in greater quantities than is agree- 

 able to their normal structure, and in consequence inevitable 

 anomalies take place in their vital action. 



