MOUNTAINS AND FJELDS. ifci 



a continuous zone, but in extensive patches, some higher, 

 some lower, all within a definite range, beneath which, 

 only a little way, it is found impracticable to cultivate it. 

 Such facts as have been cited seem, together, to warrant 

 the supposition that atmospheric and oceanic pressure may 

 possibly have some influence in permitting and preventing 

 the growth of certain plants within and beyond a certain 

 range. It may be that we can attribute to this but little 

 i iflu ;nce in comparison with the modification of light, and 

 still more the modification of heat, produced by altitude 

 above the level of the ocean, and depth below its surface. 

 But be the operation of the influence what it may; and 

 be it the case that it is only in the case of such modifica- 

 tion of pressure, light, and heat, as are strongly marked, 

 and are incidental to difference in altitude, that it arrests 

 attention, such differences as are indicated in most locali- 

 ties by differences in barometric phenomena have come to 

 be valued in investigations of the natural history of these 

 plants. 



The following is a summary of observations of the kind 

 made in Norway, for which I am indebted to Dr Broch's 

 report : 



In estimating the barometric pressure of the atmosphere 

 the calculation is made of what it would be in the locality 

 at the level of the sea. The mean annual pressure attains 

 its maximum towards the south-west of the Scadinavian 

 peninsula. It has its minimum in the region from the 

 Lofoden Islands to the North Cape, descending from 758 

 mm. at Mandal to 753 at the place last mentioned. At 

 Christiania the mean pressure of the air is 757.7 mm. 

 Twice in the course of the last forty years it has been 786 

 mm., and it has been seen as low as 721 mm. 



In winter the distribution of the pressure accords as a 

 general rule with what it is on the average for the year. 

 Greatest towards the south-east, the pressure decreases 

 towards the south-west, the isobaric line passing through 

 localities with equal barometric indications of atmospheric 



