ANATOMY OF SOME PLANTS OF A PROVINCE IN IOWA 
77 
Gross structure: Oblong to ovate; minutely pubescent. 
Histology: Subcentric (fig, 12, plate KI). 
Epidermis, both sides about equal in size, small; outer wall of upper 3 times as 
thick as inner wall; lower with walls of equal thickness. Upper wall with tri- 
chomes. 
Stomata slightly depressed with interior cavity prominent. 
Palisade parenchyma consisting of three upper and two lower layers; slender cells; 
occupies 3/4 parenchyma space. 
Spongy parenchyma of two layers, resembling the palisade but twice as broad. 
Little air space. 
Summary: The protective characters here seem to be the trichomes and the position 
of the stomata. Photosynthetic activity would seem to be prominent, according to 
the space provided for it. 
Lycopus virginicus L. 
Habitat: Alluvial basin; moist soil. 
Orientation and arrangement: Ascending: petioled; opposite. 
Gross structure: Ovate to ovate-oblong; puberulent. 
Histology: Bifacial (figs. 14a, 14&, plate XI). 
Upper epidermis thick- walled on outer side; lower epidermis uniformly thin-walled; 
wall of outer epidermis from a dry habitat twice as thick as that of a leaf from a 
moist habitat. 
Palisade parenchyma i layer in leaves from a moist habitat; 3 layers in leaves from 
a dry habitat 
Spongy parenchyma loose; occupies about the same space in each case, but equiva- 
lent to 2/3 the parenchyma space in the leaf from moist habitat and to 2/5 the 
parenchyma space in the leaf from dry habitat. 
Stomata depressed in leaf of dry habitat ; on level of epidermal cells in the other 
case. 
Summary: The leaf from the dry habitat shows a thicker epidermal wall, depressed 
stomata and greater palisade tissues, indicating better conservational tendencies. 
Scrophulariaceae 
Mimulus ringens L. 
Habitat: Alluvial basin; wet soil; near ponds. 
Orientation and arrangement: Horizontal to ascending; sessile; clasping; opposite. 
Gross structure: Oblong to lanceolate; glabrous. 
Histology: Bifacial (figs. 15a, 15&, plate XI). 
Variable epidermis; large-celled; fig. 15a, walls uniformly thin; fig. 15&, walls 
thickened on the outside. 
Palisade parenchyma in fig. 15a, one layer; in fig. 15&, two layers. 
Spongy parenchyma occupies about 1/2 parenchyma space in both figs. 15a and 
15&, though the cells are nearly twice as long in fig. 15a as in fig. 15&. 
Stomata near surface level. 
Summary: Leaf shown in fig. 15a has no conservational devices; leaf in fig. 156 has 
evidently developed in this direction as shown by the thickened wall of the epidermis. 
Compositae 
Vernonia novehoracensis Willd. 
Habitat: Alluvial basin; moist soil. 
Orientation and arrangement: Horizontal to ascending; alternate; short-petioled. 
Gross structure: Long lanceolate to lance-oblong; more or less pubescent beneath. 
Histology: Subcentric (fig. 27, plate XIV). 
