2o6 THE LIFE OF THE PLANT 



partition of the same cellulose that forms the external 

 walls. A similar process of division takes place in each 

 of the newly-formed cells after it has reached maturity, 

 and so on. In the end a whole series, a whole filament, 

 of cells is formed out of a single cell. 



Such is the process of division in the simplest cases 

 observed, but in most cases it takes place a little 

 differently. Scientists were struck by the fact that 

 during the growth of tissues in the highest plants, one 

 has never the chance of observing the above-mentioned 

 gradual ingrowth of a new partition into the cell 

 cavity. The partition seemed to appear almost in- 

 stantaneously, but on closer investigation they found 

 out that here also it is formed gradually, though in a 

 little different way. This became apparent when due 

 attention was paid to a part of the cell we have already 

 mentioned more than once, and upon which we shall 

 now dwell. This is the cell nucleus, to which whole 

 volumes have lately been devoted. In Spirogyra we do 

 notice that the process of cell division is preceded by 

 the division of the nucleus, but in most cases the con- 

 nexion between the two processes is closer still. The 

 division of the cells is preceded by a series of changes 

 which take place in the nucleus with invariable uni- 

 formity, and, what is very curious, are almost identical 

 in the cell-division of plants and of animals. Under 

 the microscope two component substances can be 

 easily differentiated in the nucleus ; the one is easily 

 stained with different colouring matters, the other 

 is not. Some time before division takes place, 

 the easily stained substance — chromatin — has the ap- 

 pearance of a bundle of tangled threads (fig. 59, A). 

 Later on these threads break into short pieces, which 

 group themselves (as is shown in fig. 59, B on the right) 

 in the equatorial plane of the nucleus. Later still these 

 pieces, of which there are usually a definite number, 

 split into halves and are drawn towards the poles of the 



