Photoperiodism is the name given to a plant's flowering response to relative length of day and night, and this response is the basis of grouping plants as long day, short day or day neutral, which supports Statement (I). Among crop plants, wheat and oat flower only when day length exceeds a critical value, placing them firmly in the long day group, which supports Statement (II). Neither statement can be rejected on this basis. \[\boxed{\text{Both statements are correct}}\]