in the Year 1835, in reference to the Physiology of Plants. 339 



Of inorganic substances which have been found in plants we 

 can only mention those remarkable either by their rarity or 

 quantity; and with regard to the latter, we must notice the often 

 mentioned paper of Radig on Digitalis, who states that he 

 has found in the herbaceous part 3*7 per cent, of oxide of 

 iron. Also the memoir of Struve* on the siliceous contents 

 of some plants. The author determined only the quantity of 

 silica in the ashes ; he should have taken into consideration 

 the proportion of silica to the vegetable substance in order to 

 render his labours of more physiological importance. Under 

 this section belongs also a part of the crystalline formations 

 discovered in plants, to which De Candolle has given the 

 name of Raphides, and, among others, those found by Nees 

 von Esenbeck in the root of Mirabilis longiflora, consisting, 

 according to him, of phosphate of lime and magnesiaf. The 

 examination of these crystals is always connected with many 

 difficulties; and we seldom succeed in obtaining the object so 

 pure as in the case which Fr. Nees von Esenbeck mentions %, 

 and as in that where the author [Marquart] obtained from 

 the stem of Aloe arborescens pure raphides in such a quantity 

 as to be able to submit them to careful analysis, which con- 

 vinced him that in this case the acid could not be of organic 

 nature, but phosphoric acid combined with lime and magnesia, 

 as in the above-mentioned raphides from Mirabilis longiflora. 

 These data do not exclude in any way whatsoever the state- 

 ments, that crystals of oxalate of lime may also frequently be 

 found in the cells of plants. Among others we may just no- 

 tice the oxalate of lime in the root of Rheum australe, which 

 I however have never been able to see under the microscope 

 in a crystalline form, but more in the state of granular ex- 

 crescences. Not unimportant to the explanation of the oc- 

 currence of salts of difficult solubility in the interior of plants 

 may be the old observation of Vauquelin § (almost forgotten) 

 which he made on occasion of analysing forty-seven varieties 

 of potato, and according to which phosphate of lime dissolves 

 in water, when some mucilaginous substance, gelatinous starch 

 or animal gelatine, for instance, is mixed with it. The state- 

 ment of Treviranus || that plants which contain raphides when 

 cut attack the knife and blacken it, may be liable to many ex- 

 ceptions; and certainly the occurrence of raphides and the 

 property of blackening the knife, stand in no relation to one 

 another. 



* De Silicia in plantis nonnullis. Dissertatio inaugural. Auctore Struve. 

 Benin, 1835. [See also the present volume, p. 13, 17. — Edit.] 

 f Physiologie der Pflanzen, vol. i. p. 47. 



X Buchn. Repert., vol. xlii. § Mem. du Mus. d'His. Nat. y vol. iii. p. 241. 

 II Flora, 1835. No. 26. p. 211. 



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