RHAMNAGE^. 67 



calycinal lobes. Petals none or inserted at the bottom of the hollows 

 which separate these lobes. Disk lining the receptacular cupule and 

 not extending beyond it or rising more or less high along the tube 

 (sometimes none or nearly so). Ovary free, except at base adnata 

 to receptacular cupule. Fruit with dehiscent or plurilocular puta- 

 men. — Shrubs with decussate branches, often thickened and spinous, 

 leaves opposite, often very reduced or none. — 6 genera. 



The thirty-eight genera are very unequally distributed over a vast 

 extent of the globe. Eight of them are met with in both worlds, 

 thirteen are limited to America, and consequently seventeen belong 

 exclusively to the old world. The Buckthorn extends over the 

 widest area and alone has been observed in all parts of the world. 

 In Oceania, it is true, it is represented by a very small number 

 of species, often doubtful; but it extends over nearly the whole 

 of America, and, in the old world, from the Cape to the North 

 of Europe, a belt of about 70°. On the other hand, there are genera 

 of very limited area, as Crwnenaria and Reissekia^ which are exclu- 

 sively Brazilian, Helinus and NoUia^ special to South Africa, and 

 Nesiota^ confined to the island of St. Helena, where, like many other 

 shrubby species, it will doubtless soon cease to exist. The 

 Trymaliece are all Oceanic, and the Phylicece are observed only in 

 South Africa and Madagascar ; Maerorhamnus belongs to this island. 

 On the contrary there are two distinct centres of vegetation, one in 

 the old world and the other in America, for Berchemia^ Sageretia^ 

 Scutia^ Coluhrina^ Gouania^ and Discaria. The greater part of these 

 latter, however, are American, as also the five other genera of 

 Colletiece, In Europe, the family is represented only by the two 

 genera Buckthorn and Jujube, 



The afiinities of the Rhamnacece are in great part established by a 

 knowledge of the mode of composition of Jussieu's family of Buck- 

 thorns from which they have been detached. The Celastracece 

 formed the greater portion of this group, and they might appear 

 very far removed from the genera of Rhamnacece then known, because 

 the latter have a concave receptacle, lined with a disk more or less 

 thick, and in the bottom of this receptacular the gynsecium is 

 inserted, while a perianth and a perigynous androecium are in- 

 serted on its margin. In this the Rhamneoe^ as perceived by 



5—2 



