All trees adjoining street sidelines in all Zones shall have their branches trimmed at all times to insure unobstructed vision eight (8') feet above street pavement level. On any corner lot in any Residential Zone, no fence, planting or shrubbery over thirty (30") inches in height above the level of the pavement at the center of the street opposite the point in question, shall be erected or maintained within twenty-five (25') feet of the intersection formed by the projections of the two street sidelines at the corner.