PROPERTIES OF VEGETABLE PROTOPLASM 357 



substance can be observed in the interior of ordinary cells. 

 It can only be seen when the protoplasm is more or less 

 filled with granules, as in their absence it is so transparent 

 that it is impossible to say whether it is in motion or not. 

 In the leaf of Elodea we find a very good instance of this 

 movement. Each cell contains a considerable quantity of 

 water, so that the protoplasm for the main part is found as 

 a layer lining the cell-wall. This layer consists of two parts, 



FIG. 149. CELLS FROM THE LEAF 

 OF Elodea. X 500. 



n, nucleus ; p, protoplasm, in which 

 arc embedded numerous chloroplasts. 

 The arrows show the direction of the 

 movement of the protoplasm. 



FIG. 160. Two CELLS FROM A 

 STAMINAL HAIR OF Trades- 

 cantia. X 300. 



The arrows show the direction 

 of the movement of the pro- 

 toplasm. 



the inner one of which contains large numbers of chloroplasts. 

 It is this layer which exhibits the movement, which can be 

 seen as a streaming motion of the plastids, the whole 

 layer flowing slowly round the cell (fig. 149). 



In other cases, particularly in long pollen-tubes, where 

 the distribution of the protoplasm is so far different that 

 bands or bridles of it cross the vacuole in various directions, 

 the movement has a more complicated course, streams of 

 granules passing along these bridles as well as along the 



