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solution in water, are at once absorbed with it by the plant, 

 and also of those substances which the plant's own agency brings 

 into solution before absorption. If the salt is a non-essential, 

 and is not consumed in the plant, as a necessary consequence it 

 remains unaltered, and the state of equilibrium which is soon 

 attained becomes permanent; hence no more of that substance 

 will be absorbed. But if it is, as in the case of essential salts, 

 consumed in the plant, and undergoes chemical change during 

 its consumption, it ceases to exist in its original form in the 

 plant, and in consequence, the state of equilibrium is being 

 continually broken, since the plant uses it up in its life and 

 growth, so that the cell-sap never contains an equal proportion 

 of the salt with the fluid outside ; a demand for more is created 

 by its disintegration, and consequently fresh supplies of it are 

 being continually taken in. Since the chemical changes which 

 go on differ in different plants, it is possible to account in this 

 way for the variety in the composition of the ash of plants 

 which have grown side by side. Water holding salts in solution 

 is principally, if not entirely, absorbed by the roots. What, 

 then, is the minute structure of a root ? and what is the exact 

 method by which plants absorb this liquid ? 



In a transverse section of the root of a Monocotyledon, 

 such as Iris, seen under the microscope, covering the ex- 

 terior we find a layer of epidermal cells, some of which 

 are prolonged into root-hairs ; inside this layer are paren- 

 chyma cells of more or less rounded form, with thin walls ; 

 in the centre we find a sort of core of narrow long cells, 

 generally with very thick walls which are altered chemically 

 as well, for they consist no longer entirely of cellulose, 

 which is the normal constituent of the cell-wall, but of a modi- 

 fication of it, viz., lignin, or wood. This core is the fibro-vascular 

 cylinder of the root, and it corresponds to the wood in a section 

 of the stem. All the intervening space between this core and 

 the epidermis is filled up by thin-walled parenchyma tissue. 



In what manner then do the roots absorb ? The soil is not 

 dry, at least never completely so, for we find moisture present 

 even in sand, and this moisture so universally present is not 



