Hydrostatic structures found in sunflowers and other many other organisms serve various functions but almost always use helical fibers as reinforcement.
Scanning electron microscope image of x-section through Helianthus annus [sunflower] vascular bundle, showing the vascular cambium between the phloem and xylem.
Scanning electron microscope image of longitudinal section of Helianthus annus [sunflower] stem showing area of vascular bundles.
“With few exceptions, nature uses the second arrangement of fibers for her internally pressurized, water-filled cylinders. These structures (often termed ‘hydrostatic skeletons’ or ‘hydroskeletons’ as well as ‘hydrostats’) have reinforcing fibers. And this particular arrangement is no rare or once-evolved thing. It occurs in the stems of young herbaceous (nonwoody) plants such as sunflowers; it provides a wrapping for flatworms (platyhelminths and nemerteans), roundworms (nematodes), and segmented worms (annelids); it stiffens the body wall of sea anemones; it determines the response to muscle contraction of the outer mantle of squids; and it’s a major functional component of shark skin. The material of the fibers varies widely, the functions of these hydroskeletons are even more diverse, but the wrapping is almost always helical.” (Vogel 2003: 409)
Vogel S. Comparative Biomechanics: Life’s Physical World. Princeton: Princeton University Press; 2003.
