What phenomenon occurs due to the inability of water to enter the stem of flowers?

The phenomenon referred to in the question—where water is unable to enter the stem of flowers—relates to the condition known as Bent Neck in Flowers. This situation arises primarily because of air bubbles that form in the stem's vascular system, preventing water from being absorbed properly.

When cut flowers are not adequately hydrated or if their stems are not properly prepared before placing them in water, this can lead to bending or drooping of the bloom. The weight of the flower head, coupled with the reduced water supply, causes the neck of the flower to bend. This is particularly common in flowers like gerbera daisies and lilies, which can exhibit this bent neck condition if not handled correctly.

In contrast, other options mentioned refer to different issues: Root Rot involves overwatering and decay of the roots, Stem Wilt pertains to the overall wilting due to lack of water uptake but is not specific to the bending issue, and Leaf Drop refers to leaves falling off, which is also unrelated to the specific mechanics of water entering the stem. Thus, the term Bent Neck specifically addresses the issue caused by the ineffectiveness of water movement in the stem, making it the correct choice.