How do you read a one-to-many relationship in both directions?
There are a lot of different graphical conventions for relationships in a data model.  See some examples in Wikipedia: Cardinalities.

The vastly most common way to represent cardinality in a diagram is to have the symbol beside an entity type represent the cardinality in the direction of that entity type.  In other words, the symbol meaning many is at the many end of the relationship.  

Specifically in your example: Each PROFESSOR teaches one or more CLASSES and each CLASS is taught by exactly one PROFESSOR.

Very rarely I've seen people do this backwards (e.g. (min, max)-notation), but if you do that you're going to confuse most people.