_ Histological Studies in the Artemisia Formation 19 
Orthocarpus luteus. Plate IV, fig. 29. . 
Rather oddly this plant possesses a leaf composed entirely 
of sponge cells closely aggregated in this species. There are 
scattered glandular epidermal hairs which give the leaf an oily 
nature. There is no indication of a cuticle or of water storage 
tissue. 
Phacelia heterophylla. Plate IV, fig. 30. 
Epidermal hairs here are very large and stiff. The cuticle is 
well developed on the upper surface, but is lacking on the lower 
side. The upper epidermis is filled with oil drops. The chloren- 
chyma is composed of a single row of long prolate palisade cells, 
and about three rows of very irregular sponge cells, each portion 
occupying about one-half of the whole tissue. The only storage 
cells present are in the narrow sheath about the vascular bundles. 
Delphinium occidentale. Plate IV, fig. 31. 
This structure is given to show an apparent deviation of struc- 
ture from that which has been found rather typical for the forma- 
tion. _This material came from the 4rtemisia formation on a 
southwest slope where the holard at 3 dcm. was 9.6 per cent, and 
yet the structure is that of a mesophyte, a rather loose palisade 
and a very open sponge. A thin cuticle covers both surfaces, and 
the bundle sheath of storage cells is well defined, structures which 
were lacking in the wet meadow form above. 
Calochortus nuttallu. Plate V, fig. 32. 
This species shows the homogeneous spongy chlorenchyma. 
The plant is a common member of the formation southwest of 
Durango in a holard of 10 per cent. The leaves-are very smooth 
and shiny and firm, due to the very thick cuticle over both sur- 
faces. Storage tissue is not present in the species. The leaves 
are long, narrow, and grass-like in form and are often folded to- 
gether on the midrib. 
Chrysothamnus graveolens. Plate V, figs. 33 and 34. 
These two figures show the structure of the dry and the moist 
forms respectively of this species. Figure 33 is from a holard 
of 8 to 11 per cent, and figure 34 from a plant growing near the 
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