THE WALLFLOWER 45 



plasm on the opposite side. Moreover, in any part of 

 the protoplasm the movement may stop altogether for 

 a time, and then start again, perhaps in the opposite 

 direction to that which it pursued at first. 



Protoplasmic movement such as this, in which 

 numerous distinct and varying currents are flowing at 

 the same time in the same cell, is called circulation. 

 In Elodea circulation tends to pass over into rotation ; 

 all the protoplasmic strands become withdrawn into 

 the primordial utricle, which then settles down into a 

 simple movement of revolution. In circulation as in 

 rotation the ectoplasm remains at rest. 



In one form or other it is probable that the proto- 

 plasm in every active cell is in movement, and that 

 power of spontaneous motion is the constant character- 

 istic of all living matter. But it is often difficult to 

 examine a cell under sufficiently natural conditions for 

 its protoplasmic movements to be observed. When 

 we come to consider the simpler plants, we shall meet 

 with several other kinds of movement executed by the 

 protoplasm. 



R THE TISSUES 



We have now been able to form some idea of the 

 essential points in the structure of a living vegetable 

 cell. Of such cells and their modifications all plants 

 consist, if we except some of the lower plants with 

 which we are not concerned at present. We shall 

 find, however, that the modifications undergone by 

 many of the cells, of which the higher plants are buiit 

 up, involve very considerable changes of structure. 



