68 CELLS IN GENERAL [CH. 



to be described later ; and the walls of the chambers con- 

 sist of some solid substance and present various degrees 

 of thickness in different cases. 



These chambers are known as cells, owing to their 

 more or less obvious resemblances to the well-known cells 

 of honeycomb, a fact which suggested the name to Hooke, 

 who applied it in 1667. 



At the very outset the student who observes and 

 compares such objects as have been named will find 

 differences of the following kinds. 



In some the cell-chambers are large, and visible even 

 with a simple lens e.g. pith, wood, &c. ; whereas in other 

 cases they are small and require the compound microscope 

 for adequate examination e.g. cork, leaf-tissue, Bean, &c. 

 Again, the cork, pith, and wood show for the most part 

 empty cavities i.e. the cells are filled with air only ; 

 whereas in the sections of the Bean, Apple, Cucumber, 

 Carrot, and Potato, or the leaf, most of the chambers 

 evidently contain something other than air, such as watery 

 fluid or various solid objects. Further, the partition- walls 

 which separate the chambers (cells) one from another differ 

 considerably in thickness and distinctness in the various 

 cases e.g. they are very thin in the slices of apple and 

 potato, or of leaf-tissue, and much more evident in the 

 wood; the shapes of the chambers also differ, by no 

 means preserving the regular hexagonal shapes of the 

 cells of honeycomb. 



From the above considerations the student will now 

 understand the following. The cavity of each cell is 

 termed the cell-cavity, the partition- walls are the cell- 

 walls, and the contents are spoken of as cell-contents. 



If we extend this preliminary examination of cell- 

 structure to sections carefully cut in definite directions 

 across the various organs of plants e.g. transverse to, or 



