ANNOTATIONS AM) ADDITIONS. 107 



combination of climatic conditions,, but also because both 

 the localities in which they originated, and their migrations, 

 have been limited. It is otherwise with the greater number 

 of genera and of families, which have their representatives 

 in all regions of the globe, and at all latitudes of elevation. 

 The earliest investigations into the distribution of vegetable 

 forms related solely to genera ; we find them in a valuable 

 work of Treviranus, in his Biology (Bd. ii. S. 47,63, 83, and 

 129). This method is, however, less fitted to afford general 

 results than that which compares either the number of species 

 of each family, or the great leading divisions (of Acotyledons, 

 Monocotyledons, and Dicotyledons) with the sum of all the 

 phanerogamse. We find that in the cold zones the variety 

 of forms does not decrease so much if estimated by genera 

 as if estimated by species ; in other words, we find relatively 

 more genera and fewer species. (Decandolle, Theorie ele- 

 mentaire de la Botanique, p. 190 ; Humboldt, Nova genera 

 et species Plantarum, T. i. pp. xvii. and 1.) It is almost 

 the same in the case of high mountains whose summits 

 support single members of a large number of genera, winch 

 we should have been a priori inclined to regard as belong- 

 ing exclusively to the vegetation of the plains. 



I have thought it desirable to indicate the different points 

 of view from which the laws of the geographical distribution 

 of plants may be considered. It is by confounding these 

 different points of view that apparent contradictions are 

 found, which are unjustly attributed to uncertainties of 

 observation. (Jahrbiicher der Gewachskunde, Bd. i. 

 Berlin, 1818, S. 18, 21, 30.) When such expressions as 

 the following are made use of " This form, or this 



