Notes on the anatomy of Parosela spinosa (A. Gray) He 



Amelia Richardson Goodlatte 



(with plate 29) 



The synonymy of this plant is considerable and though the 

 generic name Parosela of Cavanilles has priority, in the somewhat 

 scanty literature on the species It usually appears as Dalca. It 

 belongs in the order Papilionaceae under the tribe Galegeae. The 

 species is distributed from Arizona northward to Colorado and the 

 California desert and southward to Sonora and Lower California. 

 In stature it is a small tree, sometimes attaining a height of 18-20 

 feet, with a short trunk and very numerous branches. It is 

 densely spinose, the spines being apparently modified branches, 

 and the older stems are covered with a rough scaly light brown 

 bark. The younger portions, up to stems of the third year, are 

 densely clothed with hairs, and both the stems and spines bear 

 small epidermal emergences or scales, and a {^v^ leaf-buds. These, 

 together with the numerous large glands which form noticeable 

 brown spots and protuberances on the surfaces of spines, stems, 

 and leaves, give a decidedly rough and lumpy appearance. 



The hairs are of a single type ; each consists of two short basal 

 cells and a long, pointed end-cell, the outer part of the walls being 

 cutinized, especially in the basal cells, while the remainder is 

 formed of unmodified cellulose. The small scales or epidermal 

 emergences are conical in shape, hollow in the center, their walls 

 formed of two or three layers of small, nearly cubical cells, the 

 outer ones cutinized like the epidermis. 



The system of branching proves to be one of the most inter- 

 esting of the external features. The superficial appearance is 

 almost that of a dichotomous branching, but investigation shows 

 that in every case a branch arises from a leaf axil. The apparent 

 confusion is due to the fact that the spines are really the main axis 

 transformed, while the axillary shoot, continuing to grow, takes 

 the place of the main axis and itself gives off a shoot, which, 

 developing rapidly into another branch, in its turn gives rise to a 



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