28 



LIVING MATTER OR PROTOPLASM. 



rather young cells of stoneworts (Chara or Nitellci). These cells 

 have the form of short or elongated cylinders which are often 

 pointed at one end (Fig. 16). The protoplasm is surrounded 

 by a delicate membrane which thus 

 forms a sac enclosing the proto- 

 plasm. In very young cells the 

 protoplasm entirely fills the sac ; but 

 as the cell grows older a drop of 

 liquid appears near the centre of 

 the mass and increases in size until 

 the protoplasm is reduced to a thin 

 layer (primordial utricle), lining 

 the inner surface of the membrane 

 (compare Fig. 2). In favorable 

 cases the entire mass of protoplasm 

 is seen to be flowing steadily around 



FIG. 16. A cell of a stonewort (Nitel- 

 la) showing the rotation of proto- 

 plasm; the arrows show the direction 

 of the flow, in, membrane of the cell; 

 n, nucleus, opposite to which is a sec- 

 ond ; p, protoplasm ; r, large central 

 vacuole filled with sap. 



n 



FIG. 16a. Two cells and a part of a third 

 from the tip of a " leaf " of a stonewort, 

 showing rotation of the protoplasm in 

 the direction of the arrows. 



the inside of the sac as indicated by the arrows in Fig. 16. It 

 moves upwards on one side, downwards on the opposite side, and 

 in opposite directions across the ends, forming an unbroken cir- 

 cuit. The flow is rendered more conspicuous l>v various granules 



