THE CELL 



lOS 



tangential being added respectively to the latter according as 

 the sections pass through the centre of the stem as at A, or 

 not, as at B. 



3. The Cell. — If a very thin section of a turnip 'root' is 

 examined with a microscope a kind of net-like structure is seen 

 as in Fig. 48. By further examination of slices taken in several 

 different directions, a 



i 



.S 

 0^ 



similar appearance is 

 observed in each case, 

 from which we con- 

 clude that the sub- 

 stance of the turnip 

 is composed of an 

 enormous number of 

 very small more or 

 less cubical or spheri- 

 cal compartments sur- 

 rounded by thin 

 walls. These closed 

 chambers are called 

 cells. Although they 

 vary in size they 

 are usually quite in- 



. .,, , .J , Fig. 48.— Cells from the fleshy 'root' of a turnip, a: Cell- 



VlSlUle to tne unaided wall; s cell-cavlty; n nucleus; i intercellular space. (En- 

 1 • 1 larged i8o diameters.) 



eye, bemg rarely more 



than j-J^ of an inch and not unfrequently as small as xuVt of ^'^ 

 inch in diameter. A full-grown living cell (C, Fig. 49) taken 

 from near the apex of a root or stem is seen to consist of the 

 following parts : ■ — 



(i) A thin completely closed membrane (a) termed the cell- 

 wall ; 



(ii) A continuous lining (f) of a substance known as proto- 

 plasm; and 



(iii) A central space (w), the vacuole, which appears to 



