on the Geography/ of PJants, 251 



perate zones, differ but little (} to ^); indeed, if we take for 

 the temperate zone an equal extent to that used by the author 

 for the equatorial zone, the proportions do not vary. At the 

 Cape of Good Hope, according to Thunberg's ProdromuSy the 

 CompositcB make about ^, a greater proportion than in the equa- 

 torial zone, according to M. Humboldt. This example, then, 

 shews how fallacious are the calculations in respect to parti- 

 cular countries. 



Besides, which ever method we choose, we shall always meet 

 with plants that are common to several zones or Floras. ITiere- 

 fore the question arises, what are we to do with them. In my 

 opinion, we should (in order to discover the increase of the 

 number of plants in any family, either towards the pole or the 

 equator) exclude them entirely, for, in the first place, it appears, 

 that we learn most accurately the prevalence of this or that 

 family in a climate, from the number of plants which are pecu- 

 liar to it ; and, secondly, we may, by the other method, obtain 

 a result entirely unnatural, for in a small sum-total (total- 

 summe) a family may contain some plants which are but little 

 affected by variations of climate. This remark will be ren- 

 dered clear by an example. According to the author's estimate, 

 the FiliceSy in Lapland, make -^^, in France only -,/j; from which 

 he concludes that Lapland, or the polar zone, is more favour- 

 ableto these plants than France. But, it is quite evident that 

 this conclusion is not just, because the ferns diminish from 

 the tropics towards the temperate zone ; and because, in the 

 equatorial zone, the plants of this family are rare in the more 

 elevated regions (see p. li.). This becomes even more manifest 

 from the circumstance, that in Lapland, two only out of nineteen 

 ferns found there are peculiar to it * ; whereas, in France, we 

 find a much larger proportion of ferns, which are not met with 

 in polar countries. Those groups and genera, on the contrary, 

 to which the polar zone is justly considered to be favourable, 

 for example, Carices, Saxifragce, and Rhododendraj possess in 



• PoJypodium hyperhoreum and Aspidium Lonchitis. These appear likewise 

 without the polar zone, but at such an altitude, that they cannot be ad- 

 mitted among the plants of the temperate zone^ 



S 2 



