act II. scen I. what purpose does the scene between Macbeth and Banquo serve? What evidence is there that Banquo is suspicious of Macbeth?

This short scene shows some characterization of both Macbeth and Banquo.  Macbeth asks for Banquo's support when the time comes without telling him why which shows the importance of this alliance is to Macbeth.  Banquo replies by saying that he will support Banquo with anything as long as his (Banquo's) conscience can remain clear and he won't lose any honor because of his actions.  This should show the cautious support of Macbeth given by Banquo, but also that Banquo is beginning to suspect the Macbeth has poor intentions in mind.  Both of these men have been thinking about the prophecies quite a bit.  Macbeth is inclined to take action, but Banquo would prefer to wait and see what happens.