Bb as 5s, 
Histological Studies in the Artemisia Formation 15 
of those in the upper epidermis. There are two rows of very 
close palisade, and three irregular rows of palisade-like sponge 
scarcely less open than the palisade itself. The upper epidermis 
is filled with a mucilaginous or oily cell sap. 
Enogonum flavum. Plate II, fig. 15. 
A very dense coat of tangled epidermal hairs covers both the 
surfaces of the leaf. A thin cuticle is also present. There are 
two irregular rows of prolate palisade cells on each side of a very 
regular median belt of clear storage cells. The whole structure 
is very close, and the intercellular air spaces are reduced to mere 
lines. Numerous many-pointed crystals are found in the storage 
region. The cell sap is very mucilaginous, and it retains the 
stain very tenaciously. Scarcely any variation was found in 
plants of the species in a considerably higher holard. 
Gaura coccinea, Plate II, fig. 16. 
Epidermal protection in this species consists of few scattered 
epidermal hairs and a well-developed cuticle on the upper sur- 
face. The chlorenchyma is composed of five rows of close 
palisade cells, three rows above and two beneath an irregular zone 
of mucilaginous storage tissue, composed of globose to oblate 
cells filled with a very tenacious cell sap. The upper epidermis 
is filled with a like material, but the lower epidermis is clear. 
Prolate crystal sacs are scattered through the upper chlorenchyma. 
The cells beneath the storage layer are shorter by half than the 
cells above the layer. 
Linum lewis. Plate II, fig. 17. 
The leaves of this flax are perfectly smooth with a well-devel- 
oped cuticle on both surfaces. The epidermal cells are filled with 
a very dense, dark brown, waxy or mucilaginous substance. The 
chlorenchyma is composed of four irregular rows of prolate pal- 
isade cells with very small intercellular air spaces. There is not 
a sign of internal storage tissue except a sheath of a single layer 
of globose cells about the vascular bundles. These cells, like 
the epidermal cells, are filled with a mucilaginous sap. Forms 
under slightly moister conditions showed no variation from this 
structure. 
425 
