ELEMENTS OF ORGANIC STRUCTURE. 225 



coagulates the inner membrane, and colors it yellow. 

 In the same way this membrane is tinged violet-blue 

 by chlorhydric acid. These reactions leave no room 

 to doubt that the slimy inner lining of the cell is chiefly 

 an albuminoid. It has been termed by vegetable physiol- 

 ogists the protoplasm or formative layer, from the fact 

 that it is the portion of the cell first formed, and that from 

 which the other parts are developed. The protoplasm is 

 not miscible with or soluble in water. It is contractile, 

 and in the living cell is constantly changing its figure, 

 while the granules commonly suspended in it move and 

 circulate as in a stream of liquid. 



If we examine the cells of any other plant we find al- 

 most invariably the same structure as above described, 

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

 parts. In some cases cells consist only of protoplasm 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 variety. 

 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 explained. 



Vegetable Tissue. It does not, however, usually hap- 

 pen 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 surfaces, 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 across a 

 young cabbage stalk. It exhibits the outline of the ir- 

 10* 



