ECOLOGIC SUBTERRANEAN ANATOMY OF PLANTS 
93 
Gramineae 
Phragmites communis Trin. 
Habitat: Alluvial basin; edge of water, wet soil. 
Gross structure: Long, creeping rhizome, thick, soft and spongy; scales at nodes prom- 
inent; clusters of roots emerging from nodes bearing fine secondary hair-like roots; 
rhizomes branch in several directions and at several levels; perennial (Plate XV, 
fig. h). 
Histology of rhizome (Plate XVH, fig. i): 
Primary cortex: Radius equal to 1/2 radius of rhizome; epidermal cells small, 
thick-walled; hypodermis of thin collenchyma; parenchyma large-celled, hex- 
angular, forming arches around large oval air cavities in a ring within cortical 
cylinder. 
Stele: Hypodermis, 3 rows of collenchyma; main portion of vascular cylinder com- 
posed of large thin-walled parenchyma surrounding rows of alternately arranged 
vascular bundles; vascular bundles sheathed by wood fibers; one row of small 
bundles where arches of cortical parenchyma join vascular cylinder. 
Summary: Rhizome characterized by prominent thin-walled cortical cylinder; me- 
chanical tissue reduced; vascular bundles few. 
Histology of root (Plate XVII, fig. 2): 
Primary cortex; Radius 5/7 of root radius; hypodermis, 3 rows thin collenchyma; 
parenchyma of large oblong cells with long axes radially placed; large elliptical 
air spaces; endodermis prominent, with thick outer wall. 
Stele: Composed of small thin-walled parenchyma cells with a ring of young radial 
vascular bundles in which the exarch arrangement of metaxylem and protoxy- 
lem is very distinct. 
Summary: Young root composed almost entirely of thin-walled, loosely arranged 
parenchyma with prominent air space, only a trace of mechanical tissue. 
Spartina Michauxiana Hitchc. 
Habitat: Alluvial basin; wet ground; sometimes fairly dry locations. 
Gross structure: Creeping radial rhizome; long, tough, hard; scaly; springs from a 
short, condensed base; perennial (Plate XV, fig. h): 
Histology of rhizome (Plate XVIII, fig. i): 
Primary cortex: Radial depth 3/7 radius of rhizome; epidermis small-celled, thick, 
walled; hypodermis, 7 rows of collenchyma in which occasional small vascular 
bundles are embedded; clusters of compact, round parenchyma cells alternating 
with large air spaces constitute the inner arc of the cortex; endodermis thick- 
walled. 
Stele: Sclerenchyma of 6 rows borders outer margin and hollow center of this 
cylinder; vascular bundles numerous, large, with prominent sheath of wood 
fibers; pith parenchyma relatively thick-walled; only a few cells of pith between 
bundles. 
Summary: Parenchyma and air space reduced; mechanical tissue prominent; vascular 
bundles numerous, large. 
Panicum virgatum L. 
Habitat: Alluvial basin; low, wet soil; sometimes moist; dry upland. 
Gross structure: Plant tufted, with long, creeping rhizomes; scaly, hard and tough 
perennial. 
Histology of rhizome (Plate XVIII, fig. 2): 
Primary cortex: Radius 2/9 that of rhizome; epidermal cells 4-sided, thick-walled, 
small; hypodermis, 7-8 rows of thick collenchyma; inner half of cortex composed 
of clusters of thin-walled, compact parenchyma alternating with large air spaces. 
Stele: Vascular bundles large, numerous, surrounded by thick sheaths of scleren- 
chyma; pith parenchyma of 2-3 rows separating the bundles; bands of scleren- 
