27 



that potash, lime, and silica enter as organizable substances 

 into the structure of plants. The reasons which Mr. Reade 

 mentions in support of this consist, properly speaking, only in 

 the observation, that we find in the white ash of coal the form 

 of the elementary organs of those vegetable parts which have 

 been burnt, and that this skeleton consists partly of potash, 

 lime, and silica. As far back as two years ago M. Goppert* 

 made mention of a potash and lime skeleton, which remains 

 after the combustion of plants, and exhibits completely the 

 perfect form of the cells and of the other elementary organs. 

 This occurrence of potash and lime in the form of the ele- 

 mentary organs after their combustion, is however not at all 

 of the same character as the siliceous case, which is so very 

 striking in many land and water plants ; for if those alkalis 

 and earths are present in the interior of the elementary organs, 

 they must be precipitated, on the evaporation of the moisture, 

 upon the sides, and after the combustion retain the form of 

 the cells, spiral vessels, &c. The more accurately the cells of 

 plants are divided and purified by acids, alkalis, &c. the less 

 ashes do the membranes and fibres present after combustion, 

 as frequently repeated experiments have shown: however, even 

 if the adherent alkalis and earths are separated as far as pos- 

 sible, yet all cellular membrane, and even the extremely de- 

 licate spiral fibres, exhibit a trace of ashes, and this presents 

 itself in the form of the burnt elementary organs. Thus 

 Prof. Mitscherlich found that the delicate flax fibres which I 

 had divided and purified in every possible way produced al- 

 most one-tenth per cent of such ash, which presents itself in 

 the form of extremely fine membranes partly indicating the 

 form of the fibre. The cellular tissue of the elder pith, which 

 is more difficult to purify, as the single cells cannot be com- 

 minuted by attrition, gave a far greater quantity of ash, for 

 0*5945 parts of pith produced 0*0105 of ash. In the ashes of 

 the flax, Prof. Mitscherlich found a trace of silica and also 

 potash and lime : the ashes of the elder pith contained on the 

 contrary no silica, but much lime and traces of potash and alu- 

 mine. It may therefore be admitted now almost as certain 

 that these alkalis and earths occur in the substance of the 

 parietes of the elementary organs ; but it does not there- 

 * Poggendorff's Annalen, vol. xxxviii. p. 568. 



