98 
ADA HAYDEN 
small area of large-celled pith parenchyma into which project the remnants 
of the endarch xylem. 
Summary: Parenchyma prominent; cortex relatively thick; mechanical tissue absent; 
tracheae few. 
Labiatae 
Monarda fistulosa L. 
Habitat: Moist to dry slopes. 
Gross structure: Elongated, slender, radially extensive rhizome, cross section square. 
Histology of rhizome (Plate XXIV, fig. i): 
Primary cortex: Depth 1/4 radius of cylinder; epidermis of rectangular cells with 
uniformly thickened walls; hypodermal clusters of collenchyma cells in corners 
of square stem; parenchyma cells round, thin-walled; endodermis thin-walled. 
Stele: Collateral bundles; vascular band very thin; 6-sided phloem cells protected 
by collenchyma; tracheae few; wood parenchyma small-celled; band of collen- 
chyma separates xylem from pith; pith parenchyma of large, round, thin-walled 
cells. 
Summary: Parenchyma prominent; mechanical tissue sparse; tracheae few. 
Compositae 
Vernorda fasciculata Michx. 
Habitat: Alluvial basin; low wet ground. 
Gross structure: Radially elongated, extensive rhizome with clusters of thick fascicled 
roots. 
Histology of rhizome (Plate XXVH, fig. i): 
Primary cortex: Depth 1/2 radius of vascular cylinder; collateral bundles; epi- 
dermis of rectangular, uniformly thickened cells; hypodermis, 2-3 rows collen- 
chyma; aerenchyma with branched sclerids at intervals; endodermis thin-walled. 
Stele: Collateral bundles; phloem capped with clusters of bast; xylem fascicles 
separated by thick strands of rectangular-celled wood rays; tracheae few; wood 
parenchyma thick-walled, compact; wood fibers present; primary endarch 
bundle distinct; pith aerenchyma with scattered sclerids. 
Summary: Aerenchyma prominent; tracheae inconspicuous; mechanical tissue fairly 
well developed. 
Histology of root (Plate XXVH, fig. 2): 
Primary cortex: Depth 5/6 of root; epidermis uniformly thickened; aerenchyma 
fills most of cortical space; endodermis thin-walled. 
Stele: Radial bundles; small area of pith in center; tracheae few. 
Summary: Aerenchyma prominent; cortex deep; vascular tissue limited. 
Aster azureus Lindl. 
Habitat: Hill crests and slopes. 
Gross structure: Abbreviated rhizome, hard; clusters of roots form a thick fringe along 
the sides. 
Histology of rhizome (Plate XXVI, fig. 2): 
Primary cortex: Depth 1/7 radius of root; epidermis with horny, cuticularized 
edge; 3-4 rows hypodermal cork; zone of elongated collenchyma cells. 
Stele: Bundles radial; thin-walled parenchyma bearing glands surrounds the 
phloem ring; bundles tipped with bast; xylem strands appear branched; tra- 
versed by annular rings of thin parenchyma; wood fibers strengthen xylem; 
broad wood rays of elongated parenchyma cells prominent; pith of large, rather 
thick-walled cells; primary endarch xylem distinct. 
Summary: Mechanical tissue fairly prominent; xylem compact. 
Artemisia ludoviciana (Nutt.) Riddell. 
Habitat: Hillsides. 
