IX ENGLISH AND AMERICAN FLOWERS 205 



Sphere, and are found also in Australia or South Africa. 

 The absence of such a number of the characteristic and 

 dominant groups of plants of the temperate zone from 

 so extensive and varied an area as the Eastern United 

 States and Canada, is of itself a very remarkable pheno- 

 menon, and affords a prima facie ground for treating 

 the temperate regions of the New World as a distinct 

 botanical region. 



Another feature to which botanists attach much im- 

 portance in the comparison of separate floras is the pro- 

 portionate abundance of the various orders and tribes in 

 the two countries, which, when very different, leads to the 

 general vegetation having a distinctive aspect. In this 

 respect, Europe and Eastern America differ greatly. 

 Among the most abundant and characteristic groups, 

 which every one recognises in our own country and in 

 Europe as common plants everywhere to be met with, 

 are those of the cabbage and cress tribe (Cruciferse), the 

 pink family (Caryophyllacece), the umbel-bearers (Umbel- 

 liferse), the thistle-tribe of the Compositie, the bluebells 

 (CampanulacetB), the primroses (Primulaceie), and the 

 orchises (Orchidac?e) ; but all these are much less fre- 

 quent in North America, and are usually so scarce as to 

 take little or no part in determining the special aspect of 

 the vegetation. As an illustration of this difference, there 

 are only twelve indigenous genera of Crucifer^e in the 

 North-Eastern Unitexi States with about thirty-five in- 

 digenous species, while the comparatively poor British 

 flora possesses twenty-four genera, and fifty-four species. 



Instead of these characteristic European types we have 

 in America some peculiar Rubiacege, among which is the 

 pretty creeping Mitchella or partridge berry ; and an enor- 

 mous preponderance of Compositre, including numbers of 

 non-European genera and a great variety of eupatoriums, 

 asters, golden-rods, and sun-flowers, together with some 

 of our well-known garden flowers such as Liatris, Rud- 

 beckia and Coreopsis. The milk-worts (Polygala), are 

 rather numerous, and the milk-weeds (Asclepias) still 

 more so, and these last are quite unlike any European 

 plants. The beautiful phloxes are a very characteristic 

 type almost exclusively confined to North America, and 



