ANATOMY OF SOME PLANTS OF A PROVINCE IN IOWA 75 
Summary: The somewhat thickened outer wall of the epidermis and the slightly de- 
pressed stomata show some tendency to check transpiration, but the prominent 
palisade parenchyma denotes marked photosynthetic activity. This plant not only 
lives in a fairly moist habitat, but has deep roots, so that its water supply seems 
insured. 
Rhamnaceae 
Ceanothus americanus L. 
Habitat: Dry, gravelly slopes. 
Orientation and arrangement: Horizontal; alternate; short-petioled. 
Gross structure: Ovate to oblong-ovate; somewhat pubescent. 
Histology: Centric (fig. 8, plate X). 
Epidermis: Thin-walled, the outer walls hardly thicker than the inner; cells small. 
Lower epidermis in scallops. 
Stomata small; same plane with the lower epidermis. 
Palisade parenchyma one layer on each side; lower layer rather irregular; occupies 
2/3 parenchyma space. 
Spongy parenchyma relatively large; compact; occupies 1/3 the parenchyma space. 
Summary: While this plant lives in a dry, well-drained, exposed habitat, it does not 
show such protective characters as might be expected. Nothing is prominent except 
the compactness of structure. This may be accounted for by the fact that it has a 
relatively deep root which can reach a lower water table than the roots of some of its 
associates. 
Umbelliferae 
Eryngium yuccaefolium Michx, 
Habitat: Dry soil; hill crests and slopes. 
Orientation and arrangement: Ascending; stem leaves alternate; radical leaves whorled; 
sessile. 
Gross structure: Ovate-lanceolate, cuspidate-tipped; rigid, spinose. 
Histology: Centric (fig. 16, plate XI). 
Epidermal outer wall 3 times as thick as inner wall; large-celled. 
Palisade parenchyma one layer on each side ; irregular in shape and arrangement ; 
occupies 1/8 of parenchyma space; large-celled. 
Spongy parenchyma cells elongated, their long axes at right angles to the palisade; 
large-celled. 
Summary: Prominent large-celled photosynthetic tissue with prominent air space. 
Epidermal walls fairly well developed. 
Primulaceae 
Steironema lanceolata (Walt.) Gray. 
Habitat: Alluvial basin; low, wet soil. 
Orientation and arrangement: Horizontal to ascending; opposite; petioles graduated 
in length. 
Gross structure: Lanceolate; glabrous. 
Histology: Bifacial (fig. 9, plate X). 
Epidermal cells large; horizontally oval; outer walls about twice as thick as inner. 
Stomata slightly depressed. 
Palisade parenchyma i layer; large, occupying 1/3 the parenchyma space. 
Spongy parenchyma loose. 
Summary: This leaf structure indicates the photosynthetic activity with slight con- 
servational tendencies, as suggested by the slightly thickened outer epidermal walls 
and the depressed stomata. 
