Update

Just spoke to a professor about my career interests, and some questions and issues I have with the courses in the next 6 months, and just 5 minutes after I left the meeting as I was walking toward my car, I realized I forgot to ask him to be my reference for the internship I mentioned in meeting.

What do I do now? Do I schedule another face to face meeting or send an email to ask for the reference? Is sending email not polite?