246 HOW CROPS GEOW. 



nucleus and the smaller granules, lies in the center of 

 the cell like a collapsed bladder. It also assumes a deep 

 yellow or brown color. If we moisten one of these cells 

 with nitric acid, the cell- wall is not affected, but the 

 liquid penetrates it, coagulates the inner membrane, and 

 colors it yellow. In the same way this membrane is 

 tinged violet-blue by hydrochloric acid. These reactions 

 leave no room to doubt that the slimy inner lining of the 

 cell or protoplasm contains abundance of albuminoids. 

 The protoplasm is not miscible with water and main- 

 tains itself distinct from the cell-sap. In young cells it 

 is constantly in motion, the granules suspended in it cir- 

 culating as in a liquid current. 



If we examine the cells of any other plant we find 

 almost invariably the same structure as above described, 

 provided the cells are young, i. e., belong to growing 

 parts. In some cases isolated cells consist only of proto- 

 plasm and nucleus, being destitute of cell-walls during 

 a portion or the whole of their existence. 



In studying many of the maturer parts of plants, viz., 

 such as have ceased to enlarge, as the full-sized leaf, the 

 perfectly formed wood, etc., we find the cells do not cor- 

 respond to the description just given. In external shape, 

 thickness, and appearance of the cell-wall, and especially 

 in the character of the contents, there is indefinite va- 

 riety. But this is the result of change in the original 

 cells, which, so far as our observations extend, are always, 

 at first, formed closely on the pattern that has been de- 

 scribed. 



Vegetable Tissue. It does not, however, usually 

 happen that the individual cells of the higher orders of 

 plants admit of being obtained separately. They are 

 attached together more or less firmly by their outer sur- 

 faces, so as to form a coherent mass of cells a tissue, as 

 it is termed. In the accompanying cut, Fig. 30, is shown 

 a highly-magnified view of a portion of a very thin slice 



