By J. Scott Angle, jangle@ufl.edu, @IFAS_VP Danny Johns is growing the same crop on the same land as his great grandfather did when he started farming in Hastings a century ago. PURPLE SWEET POTATOESBut Johns was immediately interested when University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension agent Wendy Mussoline invited him to look at purple sweet …