602 



TREES OF NORTH AMERICA 



A tree, often 50 high, with a trunk 2 in diameter, covered with rough dark brown 

 bark, and heavy irregularly arranged usually crooked branches. 

 Distribution. Dry valleys of southern Arizona and of Sonora. 



Fig. 552 



2. Prosopis pubescens Benth. Screw Bean. Screw Pod Mesquite. 

 Leaves canescently pubescent, 2'-3' long, with a slender petiole ' f' in length, and 

 pinnae l|'-2' long and 10-16-foliolate; stipules spinescent, deciduous; leaflets oblong or 

 somewhat falcate, acute, sessile or short-petiolulate, often apiculate, conspicuously reticu- 

 late-veined, |'-f ' long, i' wide. Flowers beginning to open in early spring, and produced 



Fig. 553 



in successive crops from the axils of minute scarious bracts, in dense or interrupted cylin- 

 dric spikes 2'-3' long; calyx obscurely 5-lobed, pubescent on the outer surface, one third 

 to one fourth as long as the narrow acute petals coated on the inner surface near the apex 

 with thick white tomentum, and slightly puberulous on the outer surface; ovary and 

 young fruit hoary-tomentose. Fruit ripening throughout the summer and falling in the 

 autumn, in dense racemes, sessile, twisted with from 12-20 turns into a narrow straight 

 spiral l'-2' long; seeds T V long. 



