PARKINSONIA. 



23 



PARKINSONIA ACULEATA, P. MICROPHYLLA, AND P. TORREYANA. 

 (Plate 4 and figs. 10 and u.) 



Parkinsonias are small trees which occur in this vicinity in habitats that 

 usually are distinct. /'. aatleata is found native on the lower slopes of the 



Coyote Mountains, about 

 50 miles west of Tucson, 

 but is cultivated in the 

 gardens of the city. P. 

 microp/iylfa occurs on 

 Tumamoc Hill and on 

 the low, dry hills in the 

 western portion of the 

 Laboratory domain. P. 

 lorrcya)ia is growing in 

 the wash at the western 

 base of Tumamoc Hill. 

 The three species are 

 green in all parts, from 

 \v h i c h t h e c o m m o n 

 name, fialo rcrdc, is de- 

 rived. /'. aailcata and 

 torrcyana carry more 

 leaf -surf ace, or at least 

 larger leaves, than ;;//- 

 cro/>/iylla, in which they 

 are extremely small. In 

 ^^ ^ each species portions or 



Of" \C\Sv J\ )(kr\ all of the leaves fall away 



/-XL JVS^rl V /y\U\~ during unfavorable sea- 



sons. The general struc- 

 tural relations of the 

 stem do not need special 

 notice; they will be ap- 

 parent from the discus- 



FIG. 10. Parkinsonia tnicrophylla: A, segment of stem sion of the chlorophyll 

 3-mm. in diameter; B, transverse section of woody cylinder -mi^ratus 

 to show presence of chlorophyll in wood parenchyma 



adjoining a duct and in the medullary rays. As in all the Young branches, i. e. , 

 other sketches the stippling indicates the presence of t} lose ]_ cm or l ess 

 chlorophyll. 



in diameter, arc 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. This is the maximum chlorophyll 



