Apr., 1921] 
MCNAIR — RHUS DIVERSILOBA 
185 
The secondary medullary rays, as already noted, are usually constituted 
of one row of cells. Where biseriate rays are found, it is sometimes noticed 
that they split apart tangentially while they remain intact radially. From 
this it would seem that adjacent cells of the two columns of the medullary 
ray are only loosely united, whereas those cells which constitute a radial 
row are more firmly attached. 
Besides what has already been said regarding the phloem, it should be 
added that the sieve tubes and their companion cells extend tangentially 
and build approximately alternating bands with the layers of phloem paren- 
chyma cells, as in the stem section of Aristolochia Sipho (27). The phloem 
apparently has but little starch, which is found deposited chiefly in the 
medullary rays. These cells also give a distinct reaction for tannin with 
ferric chloride. 
Morphology and Anatomy of the Root 
The root system in its ramifications resembles the crown, in that com- 
paratively few strong branch roots are formed which carry the fine, inter- 
laced roots. The spread of roots depends largely upon the nature of the 
soil, and upon the supply of food and water. There is a strong tendency to 
form long lateral roots, particularly in shallow soil. Propagation by layering 
is very frequently made use of naturally by the plant to insure its food supply 
and reproduction. The fine, interlacing rootlets are dark brown in color 
and are covered with fine root hairs of a lighter color. The apical tips of 
the rootlets are light yellow or colorless for several millimeters. 
As in other roots, after the secondary phloem is formed the cambium 
soon takes on a circular form in section, and behaves in the formation of 
xylem and phloem exactly as in the stem (PI. Ill, ^g. 2). 
The wood of the root is less firm than that of the stem; there exist nu- 
merous large bundles, the fiber cells are less strongly thickened, the medul- 
lary rays are broader, being indeed commonly composed of two layers of cells. 
Morphology and Anatomy of the Flowers 
Rhus diversiloha is strictly dioecious, so far as my observations go. 
The male and female plants begin to bloom at about the same time. At 
Berkeley, California, but few of the flowers were open April 4, 191 5. The 
next spring the plants near the Greek Theater at Berkeley bloomed mostly 
between March 22 and May i. In 191 7 at Pasadena I noticed some male 
plants at the foot of the Mt. Wilson trail in bloom on the fifth of January. 
February 28, 191 7, the plants of both sexes were just starting to bloom in the 
Arroyo Seco, south of the Colorado Street bridge, Pasadena. In spite of 
their yellow-green color, the flower panicles are conspicuously displayed as a 
result of their size and their accumulation on the ends of the twigs. The 
presence of the staminate flowers is made very noticeable by their fragrant 
jasmine or hyacinth aroma. The pistillate flowers, on the other hand, 
