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ADA HAYDEN 
Histology of rhizome (Plate XXI): 
Primary cortex: Depth 1/5 radius of root; hypodermis of thin-walled cork cells 
occupying 1/6 cortex; thick- walled parenchyma forms a band around phloem; 
endodermis not distinct. 
Stele: Collateral bundles; phloem cells 4- to 6-sided; 3-4 strands of xylem extend 
from the center of the root radially outward, alternating with broad radii of 
thin-walled oval to square parenchyma cells. 
Summary: Parenchyma prominent; mechanical tissue undeveloped; tracheal tissue 
proportionally small; cork well developed. 
Rosaceae 
Potentilla arguta Pursh. 
Habitat: Dry, rocky, gravelly or alluvial soil. 
Gross structure: Root tap, fibrous; thick, hard, tough; perennial. 
Histology of root (Plate XXH, fig. i): 
Primary cortex: Depth 1/6 radius of root; cork hypodermis, thick-walled, occu- 
pies 1/2 of cortex; thick-walled, large-celled, angular parenchyma. 
Stele: Radial bundles separated by broad rows of oval-celled parenchyma pith 
rays which radiate from the center of the root, forming fan-shaped terminal ex- 
pansions the edges of which extend around the phloem; phloem thin-walled; 
4- to 6-sided; xylem in several annular rings; wood parenchyma thick- walled ; 
wood fibers are scattered among the wood parenchyma and form solid rings at 
termination of yearly growth; tracheae large. 
Summary: Protective cork well developed; tracheae large and numerous; mechanical 
tissue in form of wood fibers prominent. 
Leguminosae 
Petalo sternum candidum Michx. 
Habitat: Dry prairie slopes; near base of hill commonly, while P. purpureum occupies 
ridges. 
Gross structure: Root thick, tough; deep tap with prominent secondary roots; tuber- 
cled; perennial. 
Histology of root (Plate XXH, fig. 2): 
Primary cortex: Depth 1/6 radius of root; cork hypoderm occupies 1/4 of cortex; 
parenchyma large, angular, fairly thick-walled cells; endodermis not distinct. 
Stele: Bundles collateral; clusters of bast lie within the older, and around the 
young, phloem; these tissues are enclosed by wood rays which pass as radii 
from the center of the root toward the bark, joining in arches around phloem ; 
xylem with irregular clusters of large tracheae; few small wood parenchyma 
cells; compact, small wood fibers prominent. 
Summary: Cork prominent; parenchyma little; mechanical tissue in form of bast and 
wood fibers, forming a tough, compact root. 
Baptisia leucantha T. and G. 
Habitat: Alluvial basin; moist, subject to drought; perennial. 
Gross structure: Long, thick tap root with horizontal surface, fleshy branches; tough; 
tubercled; perennial. 
'Histology of root (Plate XXHI, fig. i): 
Primary cortex: Depth 1/2 radius of root; thin band hypodermal cork; large oval- 
celled starch parenchyma with scattered clusters of bast cells; endodermis not 
distinct. 
Stele: Radial bundles; several concentric zones of bast cells laid down in clusters 
bordering the new phloem and lying within and around the older phloem; 
broad rows of wood rays of long parenchyma cells extending radially into cortex, 
