342 



GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



Obs. In the preceding table, and in that which follows, species that range 

 to several zones are enumerated in each. The proportionate numbers of the 

 second table are found by dividing the whole Plianerogamce of a district by 

 the numbers of each family in that district, and they may, therefore, be con- 

 sidered as denominators of fractions having 1 for a numerator. 



The proportions vary remarkably in different districts. The predominance 

 of Compound Flowers, Leguminous and Rosaceous plants in the Prairies, 

 combined with the paucity of Saxifrages, Gentians, and Ericaceous plants, 

 affect the proportions of the other families materially. The Grasses, as 

 might be expected, are more numerous in the Prairies than elsewhere, with 

 the remarkable exception of the Polar Zone, in which the Graminece form 

 one-seventh of the species, and in conjunction with the Cruciferce, Cari/o- 

 phyllece, and Saxifragcce, constitute more than half the Plianerogamce. The 

 small numbers of Asters, Willows, and Carices, on the Pacific coast, modify 

 the numbers of that district. 



