ECOLOGIC SUBTERRANEAN ANATOMY OF PLANTS 
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parenchyma thin-walled, compact, with oval areas filled with very large paren- 
chyma cells, 6-8 times the size of the round parenchyma (these areas show 
signs of breaking up and will probably give rise to air cavities) ; endodermis with 
thickened inner wall. 
Stele: Parenchyma of small angular cells; bundles radial; a ring of large proto- 
xylem cells lying within radial strands of metaxylem. 
Summary: Mechanical tissue undeveloped; parenchyma prominent; tracheal vessels 
large. 
Polygonaceae 
Polygonum Muhlenhergii (Meisn.) Wats. 
Habitat: Alluvial basin; muddy or dry places, rarely in shallow water. 
Gross structure: Root thick, descending, tough, smooth; rootstocks branching; scaly, 
branching from root at different levels; horizontal, radial extension; perennial (Plate 
XV, fig. a). 
Histology of rhizome (Plate XX, fig. i): 
Primary cortex: Depth i/6 radius of rhizome, epidermis thin-walled; rectangular 
cells; hypodermis, several rows of cork; aerenchyma occupies 9/10 of cortical 
space. 
Stele: 1/6 radius of rhizome; bundles collateral; bast forming a slender zone bor- 
dering phloem; phloem cells large, 6-sided; xylem with large tracheae; wood 
parenchyma 4- to 6-sided, compact, thick-walled. 
Pith: Depth 2/3 radius of rhizome; homogeneous aerenchyma. 
Summary: Vascular cylinder forming a narrow, compact zone; remainder of stem com- 
posed of aerenchyma. 
Histology of root (Plate XX, fig. 2): 
Primary cortex: Depth 1/4 radius of rhizome; hypodermal cork fills 1/5 of cortical 
area; large-celled, thin-walled parenchyma fills 4/5 cortical area; endodermis 
not distinct. 
Stele: Collateral bundles; cone-shaped rays of old phloem surrounded by clusters 
of sclerenchyma extend into the cortical parenchyma, young phloem of rectangu- 
lar cells adjacent to cambium; xylem forms a solid, pithless cylinder of large 
open tracheae and small, thick-walled, 4- to 6-sided wood parenchyma; the ex- 
arch character of bundle is shown in the small primary cylinder. 
Summary: Parenchyma of cortex thin-walled with thick protective layer of cork; 
little mechanical tissue in cortex; relatively thick, compact wood parenchyma cells 
form a solid cylinder. 
Ranunculaceae 
Ranunculus delphinifolius Torr. 
Habitat: Ponds, rooting in mud; stems and leaves floating. 
Gross structure: Slender, fascicled roots; succulent; perennial. 
Histology of root (Plate XX, fig. 3) : 
Primary cortex: Depth 4/5 radius of root; epidermal walls slightly thicker than 
walls of parenchyma; parenchyma cells large, oval to round, thin-walled, spongy; 
air cavities at intervals, endodermis walls of uniform thickness. 
Stele: Vascular bundles radial; protoxylem and metaxylem distinct; tracheal 
tubes small. 
Summary: Parenchyma prominent, thin-walled; vascular tissue poorly developed; 
mechanical tissue absent. 
Saxifragaceae 
Heuchera americana L. 
Habitat: Moist to dry slopes; upland. 
Gross structure: Thick, irregularly branched, tough rhizome with small secondary 
roots; perennial. 
