GENERAL DISCUSSION OF GROWTH 



215 



The enlargement of each cell begins with the stretching of the cell wall by 

 turgor, and the effect of this stretching becomes subsequently established by 

 the deposition of new layers of cellulose. Traube's artificial cell is closely 

 analogous to the Uving cell in some respects. If a drop of gelatine is introduced 

 into a tannin solution, a precipitation membrane of gelatine tannate is formed 

 at the surface of the drop, and the cell thus artificially produced begins to 



Fig. 98. — Horizontal microscope. 



enlarge. This enlargement can be explained only by supposing that the gelatine 

 extracts water from the tannin solution; the outward pressure thus produced 

 causes a stretching of the membrane, which becomes ruptured at many places. 

 Through the small openings thus formed the gelatine once more comes into 

 contact with the tannin and the precipitation membrane is reformed, when 

 the process is repeated. 



