56 FORESTRY Otf NORWAY. 



plant is, and must be, as much dependent on them as upon 

 the others/ 



He goes on to say: 'The operation is as yet a com- 

 plete mystery to us, and many of the at present wholly 

 incomprehensible conditions in extension and distribution 

 of species may sooner or later find sufficient explanation in 

 these influences.' Since this was written, the carefully 

 made and well digested observations of Darwin have 

 thrown no little light upon the subject, and introduced a 

 method of study which is likely to throw yet more upon 

 the subject in all its bearings. 



' We find again/ says he, * indications of the undoubted 

 fact that the distribution of all plants is naturally regu- 

 lated by law, but what laws we cannot evolve, and it looks 

 as if it were wholly the result of caprice that particular 

 plants are distributed widely over the globe, while others 

 must be cribbed in the narrowest spot, as, e.g., the Wulfenia 

 found only on the Corinthian Alps ; that particular 

 families like the Compositae flourish abroad over the whole 

 earth, while others like poppies and the palms only occur 

 between very definite degrees of latitude on either side of 

 the equator, the Protoceae only in the southern hemisphere, 

 the cactus tribe only on the western half of the earth. 



* Just as inexplicable is the mode of distribution of the 

 families of plants. While the palms diminish in numbers 

 from the equator into a higher latitude, the Compositae 

 attain their highest development in the zones of mean 

 temperature, their number of species diminishes from 

 these in both directions equally towards the equator and 

 towards the pole ; while finally, the grasses increase con- 

 stantly from the equator towards the pole. 



1 Having spoken of the increase of grasses as we proceed 

 from the equator towards the poles, it is necessary that I 

 should explain the mode of consideration according to 

 which the distribution of the families is usually deter- 

 mined. Of sedges, to take that family as an illustration, 

 the species found in the flora of France amount to 134 ; 

 the species in the flora of Lapland, on the contrary, only 



