1907] HOLM—RUBIACEAE I7I 
both faces of the blade, and the lumen of the cells is much wider on 
the upper than on the lower face. The stomata (figs. 12, 13), which 
are confined to the lower face, are level with the epidermis; they have 
mostly two subsidiary cells parallel with the stoma and the air 
chamber is wide, but shallow. No hairs were observed. The chlor- 
enchyma is differentiated into a palisade tissue of two strata and a 
pneumatic tissue of four layers with broad intercellular spaces (fig. 14). 
Cells with raphides were observed in the palisade tissue, whose cells 
diminish in size above the larger veins and become roundish. An 
almost colorless tissue surrounds the midrib completely and is col- 
lenchymatically thickened below this, but otherwise the veins have 
no mechanical support, since no stereome is developed. The mes- 
tome strands are collateral, and the median is very broad, with a large 
group of leptome and about three rows of vessels; a thin-walled 
parenchyma sheath surrounds each mestome bundle. 
The petiole.—The cuticle is wrinkled and the outer walls of the 
epidermis moderately thickened. Very thick-walled bicellular hairs 
occur along the sides of the petiole, while at the base, and especially 
upon the inner face, numerous glandular hairs (fig. 14, b) were 
observed. Similar hairs were also found along the upper margins 
of the minute stipules. The chlorenchyma is quite open and con- 
tains only a little chlorophyll, but many raphides. A single, broad 
mestome bundle occupies the center; it is collateral and surrounded 
by a colorless, thin-walled sheath. The local thickenings of epider- 
mis observed in the blade do not occur in the petiole. 
The characteristics of Mitchella, therefore, are the structure of 
the epidermis of the leaf-blade; the long and slender glandular hairs; 
and the secretory, thick-walled cells inside the endodermis of the 
stem. The peculiarity noticed in some of the roots, where the lateral 
branches remain enclosed within the cortex for some time, is hardly 
to be considered as characteristic of the genus, since it was not found 
to be constant. 
DiopIA TERES (SPERMACOCEAE B. et H.) 
A seedling is shown in fig. 15. The primary root is quite long, 
sparingly hairy, and the lateral branches short. The hypocotyl is 
very distinct, erect and hairy, especially above, and the epigeic coty- 
