No I am not smart enough to have come up with this.
End grain I.D. has been around a while. The wood cells of end grain all form different characteristics in each specie. It's like a fingerprint, no two species are alike. It is very difficult to become adept at.
What makes it easier is having a pretty good idea what the specie may be, such as in our case. Using bark, leaves, and other such info can help a great deal, but you don't always have a leaf, or a fruit, etc.
The sample is easiest collected from the end of the log. Whatever the method you use to get it, the sample must have, or must be able to produce, a "slice" of end grain, like a piece of glass. Not as in the end grain fibers were "torn" apart as with a chainsaw cut.
You don't have to worry about collecting it so finicky though. Just get me a thin chunk and I can extract a shaving that'll have cleanly sliced cells.
I do use photos from various university websites etc. when i do not have an actual piece of sample wood. Over the past 3ish years we have purchased wood sample kits from various sources which are assembled for this very purpose. Of course we have also made our own from our on local species and also wood we have traded for.
Rick, you should get your hands on a book called Understanding Wood, by Bruce Hoadley
. Make sure it's the latest edition I believe there are two. Mine says volume II. We use his Wood Identification book as part of our I.D. library, but everyone who is first becoming interested in using wood at any level or phase of processing, will benefit greatly from reading it, and going back to it again and again for reference.
It will open your eyes to the complexities of understanding the biology of trees, and how and why wood acts and reacts the way it does. If you can also get his Wodd Identification book do so, but if the budget is only set for one right now, get Understanding Wood first.
I can gather a list of sources for you where you can purchase end grain samples whenver you get to that point. Warning: it is not cheap nor easy.