PARKINSONIA. 



23 



usuallv are distinct. 



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 



P. aculcata 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. 

 microphylla occurs on 

 Tumamoc Hill and on 

 the low, dry hills in the 

 western portion of the 

 Laboratory domain. P. 

 for reran a is growing in 

 the wash at the western 

 base of Tumamoc Hill. 

 The three species are 

 green in all parts, from 

 which the c o m m o n 

 name, palo vcrde, is de- 

 rived. P. aculcata and 

 torrcyana carry more 

 leaf -surf ace, or at least 

 larger leaves, than mi- 

 crophylla, in which they 

 are extremely small . In 

 each species portions or 

 all of the leaves fall away 

 during unfavorable sea- 

 sons . The g'eneral struc- 

 tural relations of the 

 stem do not need special 

 notice; they will be ap- 

 parent from the discus- 



FIG. 10. Parkinsonia microphylla: A, segment of stem sion of the chloroph}'!! 



3 mm. in diameter; B, transverse section of woody cylinder o DD n r of US 



to show presence of chlorophyll in wood parenchyma 



adjoining a duct and in the medullary rays. As in all the Young" branches, /'. e. , 



other sketches the stippling indicates the presence of f] 1O q e i cm or i css 



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 

 denned 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 



Qocfo 



Oo' 



