Digital BW, The Print

I've been taking a couple bookbinding classes that have been great 
fun.  I'd like to put together a couple photobooks with what I've 
learned.

My question is on roll paper, does the grain direction run the length 
of the roll or across it?  Is this too simple of a question and the 
answer varies from roll to roll, mfg to mfg?

The reason I ask, is the instructor said that paper grain should run 
parallel with the spine of the book and I'm looking into available 
paper sizes for some experiments.  Roll paper seems the best option.

Thanks,
Earl