What IS a "plant track"?

[BIOHEAD]

Jeffrey:

I've been in Botany for at least two decades, and do not recall ever having
heard the expression "plant track". What is this thing, that is so
out of style that nobody carries them?

                                     Thanks, 
                                                Ellmore
                                                Biology
                                                Tufts University
                                                Medford, MA