28 STRUCTURAL BOTANY 



through any fully formed organ, when seen under the 

 microscope. The network of walls enclosing the 

 cavities strikes the eye at once. We do not at first 

 particularly notice the contents of the cavities, but 

 the research of the last half century has shown that 

 it is the cell-contents, after all, which are the most 

 important part of the cell ; it is the contents which 

 form the wall, not vice versd, and in many plants the 

 cell-contents are quite able to grow and increase 

 without any wall at all, while the cell-wall without 

 its contents is a dead shell, incapable of growth or 

 activity of any kind. 



a. General Structure of the Cell 



We will now shortly consider the structure of a 

 single cell, and we will begin by describing one from 

 quite a young part of a plant, such for example as the 

 bud at the growing end of a branch. 



A young cell (se.e Fig. 14, A), like one of those of 

 which a growing-point is formed, is surrounded on the 

 outside by a delicate but firm and elastic membrane, 

 the cell-wall, by which it is separated from its neigh- 

 bours. The wall consists chiefly of a body called 

 cellulose, which is chemically very similar to starch, 

 and is composed of the same chemical elements (carbon, 

 hydrogen, and oxygen) in the same proportions. 1 



The strength and elasticity of all parts of the plant 

 are ultimately due to the cell-walls, which serve as a 

 firm supporting framework for the whole structure. 

 In such young parts as we are now considering, how- 



1 The formula is CJI 10 S . 



