448 



P1COTYLEDONKS. 



with one style and one erect ovule in each loculus. The fruit is 

 most frequently a drupe. The embryo is large, often green or 

 yellow, with endosperm. 



Rhamnus (Buckthorn) has a juicy drupe with 3 (2-4) stones, 

 surrounded at the base by the persistent portion of the receptacle ; 

 the disc is thin. R. cathartica (common Buckthorn) : dioecious, 

 with opposite, serrate leaves. R. frangula (Alder Buckthorn) : 

 flowers > , with scattered, entire leaves. Ceanothus (N. Am., with 

 richly-flowered inflorescences and a fruit closely resembling that of the 

 Euphorbias). Phylica, Pomaderris (Austr., fruit a capsule). Zizyphus, Paliurus, 

 Colletia (S. Am.) are thorny shrubs ; C. gpinosa has thorny shoots with small, 

 caducous leaves ; the seedling has normal foliage-leaves. Others climb by 

 tendrils as in the Ampelidacese, e.g. Gouania. 



FIG. 482. Kliamnus cathartica: A long-styled -flower; pet petals; B short-styled 

 cJ-flower; C long-styled ? -flower ; D short-styled $ -flower (after Darwin). 



475 species, 40 genera ; chiefly in temperate and tropical climes. Some are 

 medicinal plants, the bark and fruit having purgative properties (the bark of 

 Rhamnus frangula and " Cascara Sagrada " from the bark of E. piirshiana are 

 officinal). The fruits and seeds of others are edible, for example, the fruits of 

 Zizyphus lotus, Z. vulgari*, Z. spin a Christi, etc. Green and yellow dyes are 

 obtained from the fruit of R. cathartica, iufectoria and others (Avignon grain). 

 Ceanothus-, Rhatnnus- and evergreen Plnjlica-species are ornamental shrubs. 



Family 18. Thymelaeinae. 



Exclusively trees or shrubs with simple, entire, scattered leaves 

 without stipules. They have a strongly perigynous, regular, 4- 

 inerous flower. The receptacle (often coloured) envelopes a simple 

 gynoeceum formed of 1 carpel and with, in most cases, 1 ovule, bear- 

 ing on its edge 4 (or 5) petaloid sepals and, but rarely at the same 

 time, small, scale-like petals. The corolla is most frequently 

 entirely wanting (and hence these plants were formerly reckoned 

 among the Monochlamydeas) ; frequently only one of the 2 whorls 

 of stamens, which are situated on the inner side of the edge of the 

 receptacle, is developed. The fruit is most frequently a \-seeded 



