. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. THE VEGETABLE CELL. 25 with its substance. The higher the degree in which the latter occurs, the harder the membrane becomes, as is shewn by the relation of the heart-wood to the sap-wood, and in a still greater measure in many seed-coats of a bony consistence, e, g, the peri- carp of Litfiospermum, which contains much lime, the epidermis ot Equiseturti and Calamus^ in which a great quantity of silica is deposited. However, we are without any accurate knowledge of these conditions, in spite of the countl
. Principles of the anatomy and physiology of the vegetable cell. Plant cells and tissues. THE VEGETABLE CELL. 25 with its substance. The higher the degree in which the latter occurs, the harder the membrane becomes, as is shewn by the relation of the heart-wood to the sap-wood, and in a still greater measure in many seed-coats of a bony consistence, e, g, the peri- carp of Litfiospermum, which contains much lime, the epidermis ot Equiseturti and Calamus^ in which a great quantity of silica is deposited. However, we are without any accurate knowledge of these conditions, in spite of the countless analyses of ashes which we possess, for these give the product of ash of the cell-contents and cell-membrane together. The deposition of organic substances is not less general than that of inorganic compounds, at least in particular layers of cell- membrane. Among these the nitrogenous are cer- tainly the most widely distributed. They do not occur in the membranes of cells which are just at the commencement of their development, for these are not coloured yellow by tincture of iodine, yet scarcely a full-grown cell is met with in which this is not the case. That these nitrogenous compounds belong, in many instances, and especially in the cells of the wood, to the series of proteine compounds, we have evidence (as Mulder pointed out) in the violet colour which hydrochloric acid produces after long oper- ation, and in the yellow colour which ammonia produces after a previous action of nitric acid. Tlie presence of these compounds explains how, accoiding to Chevandier's analysis, wood contains 0*67 to 1*52 per cent, of nitrogen. The darker yellow a cell-membrane is co- F%g,ZL loured ij nitrogen, the more Wy it withstands the action of sulphuric acid, and the more difficult it is to obtain the blue colour by the combination of this and iodine. In most parenchymatous cells, especially in the tL walfed, this blue colour usually appeal's so intensely that the original y
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