ECOLOGIC SUBTERRANEAN ANATOMY OF PLANTS 
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spreading in fan-shaped areas of parenchyma; tracheae large, prominent; wood 
fibers conspicuous among wood parenchyma. 
Summary: Cortex thick; mechanical tissue prominent; tracheae large, numerous; 
compact. 
Desmodium illinoense Gray. 
Habitat: Slopes; moist to dry. 
Gross structure: Thick tap fibrous root; branched, tough; tubercled; perennial. 
Histology of root : 
Primary cortex: Depth i/6 radius of root; narrow band of hypodermal cork; 
parenchyma thin-walled. 
Stele: Radial bundle; wide rows of long, rectangular cells form wood rays which 
extend through xylem radially to bark where they form arches around phloem; 
annual rings prominent; wood parenchyma little; wood fibers abuhdant; tra- 
cheae large but few; large protoxylem and smaller metaxylem tissues of the 
primary xylem show the exarch character of the bundle. 
Summary: Small cortex; prominent stele with much mechanical tissue in form of 
wood fibers; wood rays prominent; tracheae not conspicuous; compact. 
Violaceae 
Viola pedata L. 
Habitat: Hill crests and slopes; dry, gravelly soil. 
Gross structure: Rootstock short; erect; not scaly. 
Histology of rhizome (Plate XXV, fig. i): 
Primary cortex: Depth 1/4 radius of root; hypodermal cork 2 or 3 rows; parenchyma 
large-celled, thin-walled; endodermis not distinct. 
Stele: Vascular bundles distinct; collateral; separated by parenchyma rays which 
extend into the large pith cylinder; tracheae numerous, small; wood parenchyma 
thin-walled; pith parenchyma large-celled, round to oval; fairly compact. 
Summary: Parenchyma prominent; mechanical tissue absent; tracheae small, nu- 
merous. 
Gentianaceae 
Gentiana puberula Michx. 
Habitat: Moist slopes, upland mostly. 
Gross structure: Slender rhizome bearing fascicles of relatively thickened roots. 
Histology of root (Plate XXHI, fig. 2): 
Primary cortex: Depth 1/2 radius of root; epidermal cells small, rectangular, thin- 
walled; 2-3 rows hypodermal collenchyma; large roundish parenchyma cells, 
fairly compact; endodermis not distinct. 
Stele: Radial bundles, scattered clusters of phloem surrounded by large paren- 
chyma cells; vascular cylinder small; tracheids numerous; remains of primary 
xylem show exarch character of primary bundle. 
Summary: Parenchyma prominent, tracheae few; mechanical tissue absent. 
Asclepiadaceae 
A sclepias verticillata L. 
Habitat: Alluvial basin; low prairie, moist soil. 
Gross structure: Slender, radially extensive rhizome, bearing fascicles of thic!kened 
roots. 
Histology of rhizome (Plate XXII, fig. 3): 
Primary cortex: Depth 1/4 radius of rhizome; thick-walled, oval-celled paren- 
chyma; endodermis not distinct. 
Stele: Collateral bundles; phloem zone thin, unprotected, cells more or less 
crushed; xylem with few large tracheae; compact network of wood parenchyma; 
