72 CELL-DIVISION AND CHAMBERING [CH. 



tissues it is possible to separate the elements at once 

 by the action of strong oxidising reagents e.g. nitric 

 acid to which chlorate of potassium is added and the 

 same event is brought about more slowly by exposure 

 to the weather, as in rotting. Many fungi are also 

 known which creep in and feed upon the middle lamella, 

 excreting solvent enzymes which dissolve its substance : 

 in these cases we see an excellent justification for the 

 views given, for such fungi act in a certain sense like 

 instruments which are passed into the plane referred to 

 above and part the cells asunder. 



The importance of the above discussion to the student 

 is to put him on his guard against any such view of cell- 

 structure as might lead to the implication that individual 

 cell-chambers have been brought into juxtaposition from 

 a state of isolation : the facts are exactly the converse. 

 The true cell-structure of an organ or plant is really a 

 whole, chambered up into cells by the repeated inter- 

 position of partition- walls, and we might compare it to 

 the building of a house, if we could suppose the rooms to 

 expand and new partition -walls to be inserted across 

 them. What we must not compare it to is a building 

 made up of separate box-like compartments brought into 

 juxtaposition. 



It is true that in certain specific cases fusions may 

 occur later, by which the common wall between two cells 

 becomes broken through, and the cavities thus brought into 

 open connection, and it is by this means that longitudinal 

 rows of cells become joined into continuous pipes or 

 tubes called vessels ; but the point to be emphasized here is 

 that the wall between any two cells is primarily common 

 to both of them. 



The word "cell" has been used to mean very different 

 ideas at different periods in the history of botany. When 



