Very informative post.

It is very simple to tell the difference between hemp and cannabis when being grown. Without having to test for THC.

If you are growing hemp for rope, you trim all the branches off except for the top. This urges the plant to grow much higher. It also allows you to plant them much closer together.

If you are growing cannabis for medicinal reasons, you leave all the branches and buds on it. It will not grow nearly as high and it's base will be wider. They need to be spaced further apart.

NOTE: If you mistakenly trim all of the branches/leaves/buds off of medicinal cannabis, you will also notice people crying, pointing and showing signs of outrage. :-)