22 HOUGH'S AMERICAN WOODS. 



wood occurs as threads or bundles running through, a cellular, pith-like tissue so that 

 a transverse section exhibits the wood as dots and not in concentric rings. Leaves 

 mostly parallel-veined. Embryo with single cotyledon, or rarely two, and then alter- 

 nate and unequal. Parts of the flower generally in threes. In southern United 

 States and elsewhere in or near the tropics trees are found, such as the Palms, etc., 

 which belong to this class, but none we have to do with at present. 



Exogenous plants are subdivided into two well-marked groups or sub- 

 classes Angiospermce and GymnospermcB. The former includes by far 

 the greater part of the Flowering Plants, and most of the species repre- 

 sented in " American Woods " are representatives of it. 



ANGIOSPERMaE. 



Flowering, exogenous plants in which there is a complete pistil with 

 stigma and closed ovary containing ovules which develop into seeds at 

 maturity. This sub-class comprises many groups of plants known as 

 Orders, and such as are represented by plants which attain the dimen- 

 sions of trees, within the limits of the United States, we propose to 

 consider in the following pages : 



ORDER RHAMNACE.3E : BUCKTHORN FAMILY. 



Leaves simple, mostly alternate and with stipules small or wanting. Flowers 

 small, often polygamous and sometimes dioecious; sepals valvate in aestivation, 

 small, distinct, concave and involute in the bud or wanting; stamens as many as the 

 petals and opposite them, inserted with them in the edge of a perigynous disk lining 

 the calyx-tube, short and sometimes connected with the lower part of the ovary ; 

 pistil solitary, with mostly superior ovary, 2-5-celled, each cell with a single erect 

 anatropous ovule; stigmas 2-5. Fruit a drupe or pod with one seed in each cell and 

 not arilled; embryo large with broad cotyledons and sparing fleshy albumen. 



Order represented by small trees and shrubs of warm and temperate countries, 

 with slightly bitter juice and often nauseous or purgative fruits. 



GENUS RHAMNUS, LINNEUS. 



Leaves mostly alternate, pinnately veined, entire or dentate, petiolate, condupli- 

 cate in vernation; stipules small and deciduous. Flowers small, greenish, in axillary 

 racemes or cymes, polygamous or dioecious ; calyx campanulate, the tube lined with 

 the disk, 4-5-cleft, the lobes keeled within and deciduous ; petals small, with short 

 claw, more or less notched at apex and turned in around the stamens, deciduous ; 

 stamens with very short subulate filaments and introrse 2-celled anthers opening 

 lengthwise; pistil free, with 2-4-lobed stigma and 2 4-celled ovary, each cell contain- 

 ing a solitary, erect, anatropous ovule. Fruit a globose or oblong, blackish, berry- 

 like drupe, with fleshy epicarp, and containing 2-4 cartilaginous, 1-seeded nutlets ; 

 seeds longitudinally grooved on the back. 



Trees and shrubs of considerable economic importance, and the name Rhamnus is 

 the classical Greek name, pajuvo$, of the European Buckthorn. 



