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. Hach 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 Lear Fta. 160.—Two CrLis rrom 4 
or Elodea. xX 500. SraminaL Harr or Trades- 
n, nucleus; p, protoplasm, in which cantia. X 300. 
are embedded numerous chloroplasts. The arrows show the direction 
The arrows show the direction of the of the movement of the pro- 
movement of the protoplasm. toplasm. 
the inner one of which contains large numbers of chloroplasts. 
It is thig layer which exhibits the movement, which can be 
seen ag 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 
