Cathode rays are produced from the side of the cathode while the anode rays are produced from the side of the anode. Cathode rays are produced from cathode that is the negatively charged plate, but as they travel they ionise the gas through which they pass as per the property of the cathode rays, i.e. certain electrons get knocked out as ionization takes place(of the gas atoms), the anode rays are produced as a result of knock out of those electrons.
Hence, anode rays are produced as a result of the knockout of electrons from various atoms by the bombardment of high-speed electrons.