Fig. 8. Effect of approximately two weeks waterlogging on the formation of replacement adventitious roots at the soil surface by plants of [A] maize (Zea mays) and [B] sunflower (Helianthus annuus). In A, the roots are outgrowths of pre-existing primordia. In B, the original root system has been killed and replaced by newly initiated roots formed at the shoot base and hypocotyl. Both mechanisms generate a root system with improved access to aerial oxygen