28 EASY LESSONS IN VEGETABLE BIOLOGY. 



is, as it were, imprisoned, although certain openings, 

 or pores, may be left in the cell-wall for the pur- 

 pose of communication. There is also a concentra- 

 tion of living matter within the cell, called a nucleus, 

 and sometimes a still further concentration within the 

 nucleus, called a nucleolus, (or little nucleus.) The 

 bioplasm, also, within the cell, differs in density, that 

 next to the wall of the cell being thicker, or more 

 mucilaginous, than the rest. This latter part, or lay- 

 er, has been called the primordial utricle, or original 

 bag. Fig. 3 will give a general idea of the element- 

 ary vegetable cell. 



4. The cell- wall referred 

 to in the last paragraph 

 is composed of a substance 

 somewhat like starch, 

 called Cellulose. This is 

 often thickened by de- 

 posits inside, layer after 

 layer. When it becomes 

 solid it is known as woody tissue. Common wood is 

 made up of a number of these cells arranged side by 

 side. 



5. In cells with thin membranes, the inherent mo- 

 tion of the bioplasm (Chap. Ill, Sec. 2) can often be 

 seen with the microscope. This motion has been 

 called circulation, but it is an irregular motion of the 

 particles, sometimes slower, sometimes advancing, now 



