THE LEAF 129 



the figure which they form is termed the nuclear spindle 

 (4,5,6). 



At the centre, where the nuclear plate had existed, after 

 the division of the nuclear matter a number of very small 

 albuminous granules (microsomata) make their appearance 

 (Fig. 21, 8). They and the central portions of the spindle 

 threads fuse together to form a plate, which forms a thin 

 transverse plate of protoplasmic substance in the original cell. 

 This protoplasmic plate becomes transformed into a cellulose 

 plate, which now constitutes the cell- wall separating the two 

 daughter-cells (9). These cells increase in size, and either 

 divide again or pass over into permanent tissues. 



By this means the daughter-cells of the stomate mother- 

 cells are transformed into guard cells, the median wall split- 

 ting to form the aperture. In the same way, most cells 

 increase in number, and by this means the growth of leaves, 

 stems, and root-tips takes place. 



Every daughter-cell has therefore one-half of all the con- 

 stituents of the mother-cell ; this explains the fact that all the 

 characters of the mother-cell reappear in the daughter-cell, 

 and the inheritance of all characters from one generation to 

 another can be explained by this means. 



For we may imagine that every characteristic of a cell is 

 represented by some infinitesimal piece of matter, the atoms 

 of which have a definite relative position and movement, which 

 give it its character. Now, we have only to suppose that in 

 the cell division every such particle is divided into two, just 

 as, on a large scale, the nucleus is, and then each daughter-cell 

 will contain all these characteristic atoms, with their definite 

 structure and definite movement — will, therefore, have all the 

 characters of the mother-cell. The nutrition consists in this, 

 that the raw materials which enter the cell are attracted, now 

 by one, now by another of the constituents of the cell, and 

 adopt its specific movements, and are thus transformed into 

 the same substance (assimilated). Thus every cell of a seed- 

 ling contains in the innumerable microscopically still undiffer- 

 entiated particles of its protoplasm as many different groups 

 of bodies as the resting seed, but they have become active 

 during the germination, are continually increasing in amount, 



I 



