~ PARKINSONIA. 23 
PARKINSONIA ACULEATA, P. MICROPHYLLA, AND P. TORREYANA. 
(Plate 4 and figs. 10 and 11.) 
Parkinsonias are small trees which occur in this vicinity in habitats that 
usually are distinct. P. aculeata is found native on the lower slopes of the 
Coyote Mountains,about 
50 miles west of Tucson, 
ch,z, but is cultivated in the 
gardens of thecity. P. 
microphylla occurs on 
Tumamoc Hill and on 
the low, dry hills in the 
western portion of the 
Se ORES enrnere sn... 
se Ei f f, f Laboratory domain. P. 
ji ff, torreyana is growing in 
if the wash at the western 
i 44 base of Tumamoc Hill. 
The three species are 
green in all parts, from 
which the common 
name, palo verde, is de- 
rived. P. aculeata and 
torreyana catry more 
(~ leaf-surface, or at least 
oO larger leaves, than mi- 
crophylla, in which they 
are extremely small. In 
o oO 
ND QO each species portions or 
a all of the leaves fallaway 
t Z)8 during unfavorable sea- 
O sons. The general struc- 
Cc 
oe, ie SALES S tural relations of the 
O Cia @. stem do not need special 
6 OQAG ae 0 notice; they will be ap- 
B parent from the discus- 
Fic. 10.—Parkinsonia microphylla: A, segment of stem sion of the chlorophyll 
3mm. in diameter; B, transverse section of woody cylinder apparatus 
to show presence of chlorophyll in wood parenchyma 4 
adjoining a duct and in the medullaryrays. Asinallthe | Young branches, 7.¢., 
other sketches the stippling indicates the presence of those 1 cm. or less 
chlorophyll. : : 
in diameter, are abun- 
dantly supplied with chlorophyll, which is distributed in characteristic fash- 
ion from epidermis to pith. In general terms this distribution may be 
defined as follows: It occurs in the cortex as three separate bands concen- 
trically placed in the medullary rays of cortex and of wood, in certain of 
the wood parenchyma, and in the pith. Thisis the maximum chlorophyll 
