1901] SOUTHWESTERN CACTACEAE 49 
seldom in the root, but are present in some quantity in the cortex 
and medulla of the stem. 
OPUNTIA PHAEACANTHA Engelm.—The hypoderma is rather 
thick, of six to eight layers, the outer one compactly filled with 
crystals, which occur also in great numbers throughout the 
assimilative and medullary tissues, clustering more or less about 
the bundles, but especially prominent in and about large duct- 
like spaces just exterior to certain of the bundles in both stem 
and root (Schumann’s Arystalschldéuche). Mucilage is fairly abun- 
dant. The assimilative cells are somewhat elongated, perhaps 
less so than in other forms so far recorded. Chlorophyll is 
deepest in the outer layers, but present as well in almost all 
parts of the deeper thin-walled parenchyma. The stem bundles 
form a loose reticulated network, branching early, especially on 
the flat surfaces of the stem, forming very wide secondary medul- 
lary rays. The phloem has the usual development with a scle- 
renchyma sheath. The xylem in early parts consists almost 
entirely of smaller annular ducts with flattened rings, but later 
forms spiraled tracheids and a large amount of obliquely pitted 
fiber tracheids. 
In the root especially are seen the Krystalschlauche in a high 
state of development, with a diameter of almost 1™™. The 
crystals seem to be deposited mainly along the edges of the 
duct, which may serve also to some extent for the transfer of 
mucilage. The phloem of the bundle has a slight sheath; the 
xylem is composed of large and small scalariform tracheids and 
the usual fiber tracheids. 
OpunTIA FULGIDA Engelm.— The epidermis contains a deposit 
of crystals, a small quantity of which also occurs in the relatively 
thin hypoderma. The assimilative tissue is of cylindrical cells 
in lines, grading in the interior into large thin -walled paren- 
chyma, also chlorophyllous. Mucilage is exceedingly abundant, 
and the ducts for its accommodation and transfer are both large 
and numerous. Large crystals, loosely aggregated, occur in 
small numbers throughout the tissue. 
The bundles here remain very small through several joints, 
Mo.Bot. Garden, 
1902. 
