Vegetable Physiology. 387 



lamellce of epidermal-cells, in contact with the atmosphere, appear 

 to be always chemically changed into a substance of resinous or 

 waxy nature, which remains unaffected or is dissolved by the 

 above reagents (fig. 3 a). This conversion takes place to a very 

 great extent in some instances, especially in certain fruits, where 

 the transformed lamellae form a distinct waxy inv^estment, giving 

 the so-called ' bloom ' of plums, grapes, &c. The silica which 

 exists in the epidermis of the grasses and other plants, appears to 

 be an impregnation of the outer lamella? of the cell-wall, hardened 

 in their substance, and not a deposit inside or outside the walls of 

 the cells. 



We have now to enter upon the examination of the more im- 

 portant contents of vegetable cells, which, as was shov/n in our 

 former paper, possess the liighest interest for the physiologist, and 

 as they include the principal nutrient substances furnished by 

 plants, must be an especial object of inquiry in reference to agri- 

 culture. 



Among the cell-contents we find fluid and solid substances, and 

 some of intermediate consistence. Of these latter, the protojdasm, 

 or formative matter, is a substance of the first importance. It was 

 shown in our sketch illustrating the ordinary modes of develop- 

 ment of cells, that the production of new cells depends upon 

 this substance, and it was at the same time indicated that it 

 takes a principal share in the production of all the other contents 

 of the cells — that, in fact, it is to be regarded as peculiarly the 

 vital part of the structure. 



The example selected for illustrating the process of cell-divi- 

 sion, the Confervoid filament (vol. xvii. page 79), was chosen on 

 account of the process occurring there in a modification far more 

 accessible than usual to direct observation, both on account of the 

 size and the anatomical condition of the parts. The process 

 takes place in a manner essentially similar in the higher plants, 

 and the young cellular hairs of Flowering plants present a con- 

 dition very like that of the Confervoids. But in these and still 

 more in the cambial tissues of buds, of nascent leaves (fig. 1), 

 rootlets, and other organs, the cells are excessively small, and 

 so crowded together that the observations are rendered very 

 difficult. 



Where the cells are so very small at their birth, and their sub- 

 division is repeated rapidly befoie they have time to expand, as 

 in the nascent organs just referred to, the protoplasmic matters 

 exist in a state rather different from that in the large tubular 

 Conferva-cell : entirely filling up the cavity of the minute cell, 

 instead of forming a layer lining the cell-wall, so that the con- 

 striction here effects simply the parting of one mass of formative 



