Beschreibung:
<p>The ornamental daylily, Hemerocallis fulva (Hemerocallidaceae), possesses a short, vertically oriented basal shoot packed with a circle of root tubers that are exhausted during sprouting after dormancy. During the growth period a new circle of root tubers is formed, enabling the plant to survive the next resting phase. In shallow-planted individuals the new root circle appears just above the old one. The new root tubers show strong contractile activity and pull the cryptocorm downward. Deep-planted cryptocorms of H. fulva move upward by the growing shoot tip. During the sprouting process, a few internodes of the deeply located shoot tip elongate, and thus the new root circle appears at a distance of several centimeters from the old root circle. However, this shoot elongation only appears when the individual is positioned very deeply in the soil (facultative shoot elongation). Induction experiments make clear that the parameters (light, temperature fluctuations) that normally influence the activity of contractile roots cannot regulate root contraction in H. fulva. Contraction is a basic characteristic of H. fulva roots and always functions to pull down the vertical shoot. However, individuals of H. fulva are well adapted to secure the best soil position for survival by having two mechanisms to regulate soil depth: the pulling effect of contractile roots, and, as an emergency response, the opposite effect of upward growth of the facultative shoot elongation.</p>