GEOGRAPHICAL DISTRIBUTION 171 



logical grounds, are characterized by few genera and a 

 restricted or (if wide) discontinuous distribution. Thus 

 the Barberry family, one of the relatively primitive 

 groups of dicotyledons, contains only about lo genera 

 and over 130 species, found in temperate North America 

 and Asia, temperate South America, and sparingly in the 

 tropics; the Nymphaeaceae (Water lily family), more 

 primitive than the Berberidaceae, contains only eight 

 genera and about 50 species, of wide but discontinuous 

 distribution. In contrast there may be mentioned the 

 gamopetalous Potato family (Solanacese), with about 

 70 genera and 1,600 species, found generally on every 

 continent, and in New Zealand, Hawaii, Australasia, 

 and other oceanic and continental islands, and specially 

 abundant in the tropics; and also the still more highly 

 developed Madder family (Rubiacece), with as many as 355 

 genera and 5,500 species, also of almost cosmopolitan 

 distribution. As a final example among families of 

 flowering plants, there may be mentioned the Orchidaceae, 

 the most highly developed of the Monocotyledons, and, on 

 morphological grounds, possibly the most recent family 

 of seed-bearing plants. This family contains about 430 

 genera and over 5,000 species, of almost cosmopolitan 

 distribution, most abundant in the tropics, and gradually 

 diminishing toward the poles. The seeds of orchids are 

 very tiny, and the embryo consists of a few undifferenti- 

 ated cells. They are capable of rapid and wide 

 distribution (Fig. 78a). 



In the Nympheaceae is the relatively primitive genus, 

 Nelumbo, containing only two species, one the lotus 

 {N. luiea), in North America, the other the Oriental 

 lotus (N. nucifera), in Asia and Australasia. In the 



