Anatomical stem structures are very diverse within the family of Papaveraceae. In the present material annual rings occur in most perennial species in all vegetation zones. Rings are absent in annual species (Fig. 1), and in the bulbs of Corydalis species (Fig. 2). Ring boundaries of most species are defined by semiring porosity (6 out of 8 species) or diffuse porosity (Fig. 3). Vessels are solitary (Fig. 4) or are arranged in short (2-4 vessels) or long radial multiples (>4 vessels; Fig. 1) or groups (Fig. 5). Vessels of fast-growing individuals can be arranged in tangen tial rows (Fig. 5). Vessels are smaller than 20 pm in the bulb of Corydalis solida (Fig. 2). Earlywood vessel diameter of the majority of species varies between 30-60 pm. Diameter exceeds 100 pm in the second ring of Glaucium flavum grown in the subtropical climate (Fig. 14). Vessel density varies in the majority of cases between 200-300/mm2 (Figs. 3-5). It is only lower in the second ring of Glaucium flavum (subtropical climate; Fig. 14). Vessels contain exclusively simple perforations (Figs. 6 and 7). The shape of inter-vessel pits is very variable. They can be round (Fig. 6), laterally extended (Fig. 7), distinctly scalariform (Fig. 8), and almost annular (Papaver variegatum; Fig. 9).
Fig. 3. Distinct rings of a semi-ring-porous xylem. All cell walls are unlignified. Rays are absent. Root collar of 20 cm-high perennial hemicryptophyte, subalpine zone, limestone gravel, Mt. Ventoux, France. Pa-paver auranthiacum, transverse section.
Fig. 1. One ring in an annual plant. Vessels stand in long radial and multiple groups between rays with unlignified cell walls. Root collar of a 30 cm-high annual herb, mountain zone, ruderal site, Brian^on, France. Fumaria officinalis, transverse section.
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