II 



DISTRIBUTION OF SPECIES 



19 



'"" ! 



By an extensive comparison of floras all over the world 

 it is found that less than five per cent of the total of the 

 known species are found in more than two of these regions. 

 Families which have very few annual species show a still 

 smaller percentage (three per cent) ; while those whose 

 species are mostly trees or shrubs have less than two per 

 cent which extend to more than two regions. 



He also finds that those with fleshy fruits have a wider 

 dispersal than those with dry fruits, and those with very 

 small seeds, wider than those with larger seeds. Eighteen 

 species only are found to be spread over half the land surface 

 of the globe. There are no trees or shrubs among these ; 

 grasses are most abundant among them ; and composites — 

 the daisy and aster family — the least ! This last conclusion 

 seems very strange in view of the fact that this family has 

 its seeds so frequently provided with special means of dis- 

 persal, either by the wind or by animals. But he also points 

 out, what is now well known to botanists, that the species 

 of Compositae are not usually very widely spread ; and also 

 that several other natural orders in which the seeds are 

 usually winged for wind-dispersal are not more widely dis- 



