VI] MEANINGS OF THE WORD "CELL" 73 



Hooke applied it in 1667 he meant, as we have seen, the 

 empty cavities in the framework of cell-walls, and so the 

 word signified a mere cavity. Later on it was, and still 

 is, applied to the cell-wall, together with its living cell- 

 contents, forming a whole bounded by the ideal plane 

 which separates one cell from the other; and finally (in 

 part owing to the influence of zoology, because in animal 

 cells the cell-wall is usually not prominent) the word has 

 been applied to the living cell-contents alone, which are 

 not unfrequently met with, even in plants, as naked 

 individuals which have escaped from the cell-wall. 

 Since, however, the empty dead cell-frameworks were at 

 one time filled with living contents, we now recognise 

 that they are not complete cells, but the skeletons which 

 have been left behind when the contents disappeared ; 

 and, similarly, since we now know that the naked in- 

 dividuals without cell-walls, sooner or later acquire the 

 protective covering, the modern idea of the cell is easily 

 grasped and shown to include all the others. Since, 

 however, the cells in different parts of plants and in 

 different species undergo enormously varied changes both 

 in the contents and the cell- walls, we must fix our ideas 

 a little by selecting a typical cell for reference. 



Such a cell may be found in the earliest stage of every 

 plant, and is the only constituent of many of the lower 

 plants, the cells of many Algae, Fungi, &c. never advancing 

 beyond this primitive condition, and since we find such cells 

 again in the youngest stages of all new organs e.g. in 

 the growing-points, roots and stems, leaves, flowers, &c., of 

 Mosses, Ferns, and flowering plants we are justified in 

 taking it as the type. 



The most convenient example is obtained from a 

 section through a growing-point of any young organ of 

 a higher plant. 



