MISUTE STIiUCTUllE. 



51 



daries ; and since these boundaries are visible, no matter 

 in what direction we make our cutting, it is clear tliat 

 the spaces must be shut in on all sides. These enclosed 

 spaces are called cells, and their boundaries are known as 

 the cell- walls. 



Protoplasm. 



"Whilst looking at the parts of plants just submitted to exami- 

 nation, it must have struck j'ou that the interior of the 

 cell presents a ver^- different appearance in different cases. 

 The Potato section, for example, is not at all like tho 

 Moss-leaf section in the matter of cell-contents, and the 

 cells of the Elder-pith appear to be quite empty. We 

 shall discuss these differences presentl}-. In tiie mean, 

 time let us studj' the appearance of some cells taken fresh 

 from some part of a plant where growth is actually going 

 on — say the point of a new rootlet. If our section is taken 

 near enough to the point we shall get cells which have 

 been just formed. Such a section is xevy well shown in 

 Fig. 255. Here the cells are seen to be completely- filled 

 with liquid having a granular apiicarance, and in the 

 centre of each a rounded denser jiortion may be made out, 

 each of these again enclosing one or more smaller bodies. 

 This liquid wdiich thus fills the newly-formed cells is 

 called protoplasm (p), the large rounded central mass is 

 the nucleus [h), consisting of denser protoplasm, and the 

 smaller enclosed masses are the nucleoli {kk). 



Now let us consider Fig. 256. This is a representation of a 

 section of the same rootlet, taken a little farther back 

 from the point, so that the cells now in view are a little 

 older than the first ones. Thej' are manifestly larger ; 

 that is to sa}-, they have grown. The nucleus and the 

 nucleoli can still be made out in some of them, but tho 

 protoplasm no longer entirely fills the cell. There arc 

 now transparent spaces {vacuoles [.«.•]) which are filled 

 with water, and between these the protoplasm is seen in 

 the form of strings or bands, as well as lining the cell. 

 The water has been absorbed through the cell-wall, and 

 after saturating the protoplasm tlie excess has formed 

 the vacuoles. 



Fig. 257 shows some cells from the same rootlet taken still 

 farther back. It is clear that the change observed in Fig. 

 256 has been carried to a still greater extent. In some of 

 these cells the protoplasm is restricted to the lining of the 

 cell and the nucleus. In this figure h is the cell-wall ; 

 s, s, vacuoles ; p. protoplasm ; k, nucleus. 



It is now to be observed that the protoplasm is the essential 

 part of every living cell. Through its agency all the 

 vital processes of the plant are carried on. Every cell of 



Fijf. a.vi. 



Kit'. 'i->i. 



r7 



Fig. 25»;. 



