You can always tell the straight of grain from the crosswise grain just by tugging on the fabric, too, if it has no selvage.
If you pull and it has some give, that is the crosswise grain (or the grain that goes across the width of the fabric). If you pull and there is no give, that is the lengthwise grain (the grain that runs the length of the selvage). If you tug and it really has give, then that's the bias, with the true bias being at a 45-degree angle to the selvage.
