why is that sometimes we can not see cytoplasmic cell streaming in plant cells when using a light microscope.?

Question

so we used a light microscope to examine a Elodea leaf, i focused on a cell and observed it for 15 minutes. no cell streaming took place, why is that?

Answer 1

Cell streaming (cyclosis) is more apparent in some cells than others. Search for a cell that is carrying on the process. Focus on a few chloroplasts; better on high power (~450X). You should see some chloroplasts moving in a circular pathway close to the cell membrane.
Sometimes the cell has to be warmed up a bit to speed up the process. The electric lamp under your microscope should do this.
Search;be patient, you will find this ocurring.

Answer 2

to see the cytoplasmic streaming in Elodea cell, look here:

http://www.cells.de/cellseng/1medienarchiv/Zellstruktur/Plastiden/Chloroplasten/CP_in_Protoplasmastroemung/Wasserpest/index.jsp