CONTENTS OF CELLS. 77 



one or the other case in view, the cells appear as mere chambers and parts of 

 the growing plant-body, or as independent living organisms from which new plants 

 arise by growth. It depends, therefore, entirely upon our mode of consideration, 

 and upon the point of departure of our consideration, whether we regard the cells 

 as independent so-called elementary organisms, or merely as parts of a multi- 

 cellular plant. 



Our consideration of cells has hitherto been particularly concerned with their 

 external boundary, which is afforded by the solid cell-wall or cell-membrane ; and in 

 a larger cellular plant these walls or membranes form the solid framework, within 

 which, in the cell-chambers and partly in the framework itself, the fluid sap moves 

 and all other substances of the plant are cont3.ined. It now concerns us to 

 make ourselves more closely acquainted with the matters which are contained in 

 the chambers — in the cells. In very many cases, e. g. ordinary wood, cork, bark 

 or even old dried-up pith from shoot-axes (Elder pith), or the tissue of fallen 

 leaves, &c., we find the cell-chambers empty ; i. e. they contain either merely air, or 

 at most clear water or a few granules. The same is the case also with the integuments 

 of seeds and dry pericarps. We have become accustomed to consider such parts 

 of plants as dead or perished; since experience teaches, without exception, that 

 when the cell-chambers are empty in the manner stated, the parts grow no more, 

 that no more metabolism occurs in them, and that no new cells are formed in 

 them. They are in these respects inactive, physiologically dead, but they may be 

 nevertheless of great use in the general economy of the plant, as we shall learn 

 subsequently with respect to wood, elastic fibres, and cork. It is, moreover a 

 peculiarity of the more highly developed plants, especially of the so-called vascular 

 plants, that masses of such dead cells (contributing to the life of the plant however) 

 become accumulated. In the Mosses, Algae, and Fungi this occurs only incidentally. 

 In every living plant, however, are found layers, strands, and other aggregates of 

 living cells; i.e. such in which further growth, cell-multiplication, and chemical 

 processes of life take place. In highly organised plants, it is the soft cortex of 

 older parts, the succulent shoot-axes and leaves, the growing points of the shoots 

 and roots, the flowers, unripe fruits and seeds, which consist of such living cells. 

 In Mosses, Algae, and Fungi the whole living body of the plant generally is 

 composed of them. 



The contents of the cell-chambers in such living parts of the plant, in 

 the narrower sense of the word, may be exceedingly various. Very generally 

 there are found together with a watery fluid, the cell-sap, more or less numerous 

 starch-grains, drops of fat, small crystals, and in ripe seeds so-called aleurone- 

 grains. In green leaves, and in other green parts of the plant, green roundish 

 or polygonal granules of soft substance are particularly conspicuous: these are 

 the chlorophyll granules, which in many Algse are replaced by green bands, 

 plates, and the hke. All these contents of the living cells when suflSciently 

 magnified attract the attention at once; and up to about the year 1840 they were 

 almost the only contents which were noticed in the cell. But on more carefiil 

 observation of the interior of the cell-chambers, especially when the granular 

 structures named are not present in too great quantity, there is perceived in every 

 living vegetable cell another substance of a very peculiar kind, which generally 



