VEGETABLE CELLS. 181 



regards the original wall of the cell as a mere shell, having 

 quite a subordinate office to perform in the growth of 

 plants; and he ascribes all the vital powers of growth to 

 the eytoblast and colouring-matter of the central nucleolus. 

 He supposes the cell-membrane to arise from the action of 

 electrical currents upon mucus, and that fissiparous division 

 is caused by the presence of two centres of electrical force, 

 each giving rise to a set of currents, and producing two 

 cell-membranes instead of the original one. 1 



The first and most curious exemplification of the simple 

 cell is the fungi known as the Yeast Plant: it consists of 

 two parts, the cell-wall, composed of a matter termed 

 cellulose, and the contents of the cells, resembling fat or 

 oil. The notion that yeast was an organised living plant, 

 was at first strongly opposed by even Berzelius and Liebig ; 

 but by the microscope they have been convinced both of 

 its organisation and vitality. The scientific name by which 

 it is known is Fermentum cervisia, or Torula cervisia ; it 



Fig. 100. The growth of the Yeast Plant. 



consists of globular or ovoidal transparent nucleated cells, 

 represented in the accompanying fig. 100, and showing its 



(1) For further information on this very interesting subject, see Henfrey's 

 translation of Mohl's Vegetable Cell ; Dr. J. B Sanderson on " Vegetable Repro- 

 duction," Cyclopedia of Anatomy and Physialog^, &c. 



