27*2 SEQUOIA SEMPERVIRBNS. 



tropical forest. Along the eastern fringe of the belt, the trees that 

 remain are smaller and are mixed with the Douglas Fir (Abietia 

 Douglasii), the Bark Oak (Qucrcus densiflora) and other trees ; they 

 are also smaller at the southern limit of the belt where the annual 

 rainfall is lighter. In seeking for an explanation of this exuberant 

 arborescent growth, there can be no doubt that the climate of the 

 region has been the most important factor, not only in the formation 

 of the Eedwood forests, but in building up the other gigantic coniferous 

 trees of California. 



The climate of the coast region of California is marked by a 

 comparatively equable temperature throughout the year, the summer 

 average at San Francisco being about 15" C. (60 F.), and the winter 

 10 C. (50 F.). Two causes co-ordinate to bring about this narrow 

 fluctuation. One is the cold arctic current from Behring vStrait 

 which strikes the California!! coast in about latitude 42 IX T . and 

 continues its course southwards ; by this stream of arctic water the 

 temperature of the ocean from May to October is reduced much below 

 the average in the same latitude elsewhere ; concurrently with the 

 arctic stream, a cool wind blows uninterruptedly in the same direction 

 during the same period and in which no rain falls. The other is a 

 warm wind which blows" during the remainder of the year from the 

 south-west over the equatorial region of the Pacific Ocean charged with 

 the evaporation that is raised in prodigious quantities under a vertical 

 sun ; most of this vapour is precipitated on the country from the 

 coast to the summit of the Sierra Nevada, the precipitation gradually 

 diminishing in quantity in a southern direction to the lower Calif ornian 

 peninsula where it ceases altogether and the country is a desert. 

 This alternation of seasons is regular from year to year ; all through 

 the summer season fogs rise from the Pacific Ocean and flow inland 

 like a great level sea of vapour : the lower mountains near the coast 

 are enveloped, and further inland it fills the canons, leaving the higher 

 mountains to rise like islands out of it. It is these ocean fogs 

 that exercise so powerful an influence on the distribution and growth 

 of the Eedwood ; outside their range it does not spread spontaneously. 

 The tree is not only a lover of moisture, but to an extent hardly to 

 be believed imless seen, a condenser and consumer of moisture ; the 

 tops of the trees reach high into the sea of vapour and constant 

 precipitation from them like rain, takes place during the prevalence 

 of the fogs.* 



Sequoia sempervircns ranks second in size amongst the gigantic 

 coniferous trees of western North America. In its scientific aspect 

 and associations, it is one of the most interesting of trees, whether 

 we regard it as a surviving representative of the vegetation of a 

 former epoch that has well nigh disappeared, or look upon it simply 

 in its relationship to existing Conifene. In the geological age termed 

 the Miocene, S. sempcrvircns or a species closely allied to it was 

 widely distributed over the eastern continent in high latitudes, 



* Garden and Forest, III. 235. 



