46 RHAMNACEJE. (BUCKTHORN FAMILY.^ 



Order 20. CELASTRACEflE. (Staff-tree Family.) 



Shrubs, with simple leaves, no stipules, and small dull-colored perfect 

 regular flowers, the stamens as many as the petals and inserted on the 

 .margin of a broad disk which lines the calyx-tube. — Sepals and petals 

 imbricated. Stamens alternate with the petals. Seeds arillate. 



1. PACHYSTIMA, Kaf. 



Calyx with a short tube and 4 rounded lobes. Petals 4. Ovary free, 

 2-celled : style very short. Capsule small, coriaceous, 1 to 2-seeded. Seeds 

 enclosed in a white many-cleft membranaceous aril. — Low evergreen shrubs ; 

 leaves smooth, opposite, very shortly petioled, serrate or serrulate ; flowers 

 green, in one to few-flowered axillary cymes. 



1. P. Myrsmites, Raf. Leaves ovate to oblong or oblanceolate, cuneate 

 at base : fruit smooth. — In the mountains from New Mexico to British 

 America and westward to California. In dense clumps on wooded slopes. 

 The only other species known (P. Canbyi) grows at a single station in the 

 Alleghany Mountains of Virginia. 



Order 21. RHAUINACEjE. (Buckthorn Family.) 



Shrubs or small trees, with simple undivided leaves, small and often 

 caducous stipules, and small regular flowers. — Sepals valvate in the 

 bud ; a conspicuous disk lining the short tube of the calyx. Petals 

 clawed, mostly involute, each around a stamen in the bud, sometimes 

 wanting. Stamens perigynous and alternate with the sepals. In ours 

 the fruit is berry-like or dry, containing 2 to 4 separating seed-like nut- 

 lets, and the leaves are alternate. 



1. Rhamnus. Calyx and disk free from the ovary ; calyx-lobes erect or spreading. 



Petals small, short-clawed, or none. Filaments very short. Fruit berry-like, with 2 

 to 4 mostly indehiscent nutlets. 



2. Ceanothus. Calyx and disk adnate to the base of the ovary ; calyx-lobes connivent. 



Petals long-clawed, hooded. Filaments exserted. Fruit dry, with 3 dehiscent 

 nutlets. 



1. RHAMNUS, L. Buckthorn. 



Flowers perfect or polygamo-dicecious. Calyx 4 to 5-cleft. Petals on the 

 margin of the disk. — Leaves pinnately veined, with small deciduous stipules, 

 and greenish flowers axillary cymose or racemose. 



§ 1. Seeds and nutlets deeply snlcate or concave on the back : flowers mostly 



dioecious, solitary or fascicled in the axils. — Rhamnus proper. 

 1. R. alnifolia, L'Her. A shrub 2 to 4 feet high : leaves deciduous, 

 ovate-oblong, crenately serrate : petals wanting : fruit black, obovate, 3-lohed 

 — W. Wyoming, westward, and eastward across the continent. 



