THE AMERICAN MIDLAND NATURALIST 
(oe) 
wn 
The hairs of the stem are epidermal in origin, confined mainly 
to the ridges of the stem (Fig. 19 E.), are formed as outgrowths 
from single superficial cells. In all the hairs examined protoplasm 
was found to be present containing besides a nucleus with its 
centrally placed spherical nucleolus, granular deposits (Fig. 19 A.). 
The hairs, cylindrical in outline with a broad base gradually 
tapering toward the apex, have their surfaces marked with thicken- 
ings obliquely to the vertical axes. (Fig. 19 C.). 
LEAF. 
PETIOLE. (F1g. 20-21). 
The petioles in cross section are more or less semicircular 
in outline. The hadrome vessels are spiral and annular with 
increasing caliber toward the cortical tissue. The narrow companion 
cells are scattered among the sieve-tubes with heavy cross walls 
(Fig. 21). The pith is composed of medium-sized cells with many 
intercellular spaces. The endodermis in cross sections forms 
nearly a perfect circumference about the stele, while in longi- 
tudinal section the cells differ very much in height and thickness 
(Fig. 20-21 End.). Chlorophyll is scattered throughout the extra- 
stelar fundamental tissue as far inward as the endodermis inclusive, 
with starch grains and calcium oxalate crystals confined mainly 
to the inner part of cortex. ‘The cortical parenchyma cells increase 
in size toward the endodermis. The two lateral vascular bundles 
one on either side of the central bundle possess vessels of the same 
type as those of the latter, and nothing equivalent to an endo- 
dermis sheath. 
BLADE. (Fig. 22). 
The transverse section of the blade (Fig. 22) was made at 
about the centre of a fully developed leaf. The chlorenchyma is 
composed of a single layer of palisade cells compactly arranged 
abutting the upper epidermis, and loosely arranged parenchyma 
cells next to the lower epidermis, separated from one another 
by large intercellular spaces. The striking character of the meso- 
phyll is the abundance of chlorophyll. The layers of cells immedia- 
tely under the upper and lower epidermis, 4 or 5 rows in the former 
and 1 or 2 in the latter region, at opposite sides of the central 
bundle, are thick-walled (collenchyma) and usually devoid of 
chlorophyll. The spongy parencyhma viewed from the lower 
face has many intercellular spaces (Fig. 23), ‘he central wood- 
