On a corner lot, nothing shall be erected, planted, placed or allowed to grow in such a manner as materially to impede vision between a height of two and a half (2 1/2) and ten (10) feet above the center line grades of the intersecting streets in an area bounded by the street right-of-way lines of such corner lot and a line joining points along said street right-of-way lines fifty (50) feet from the point of intersection.