The line drawing on the left is from a book in 1978 that got me confused, curious, and started my research on how roots really grow. The drawing on the right shows how far roots travel from their trunk & beyond the dripline (canopy). The red circles are the driplines. (Based on my book: Roots Demystified, Change Your Gardening Habits to Help Roots Thrive.) The roots pictured here are of an apple tree. Look how the roots avoid the compacted soil and even the roots of another apple tree.
Let me know what you think.
NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert