SPECIALIZATION IN VEGETATION AND IN 

 ENVIRONMENT IN CALIFORNIA' 



W. A. CANNON 



The Desert Laboratory, Tucson, Arizona 



To a person who is best acquainted with a country where the 

 topography is monotonous, the cUmate the same over the region, 

 and the species of general occurrence, a visit to Cahfornia, where 

 the opposite conditions largely obtain, must reveal many things 

 which are at once novel and of much interest. It will be found, in 

 short, that, in the state, there is a climate and a physiography, both 

 very diverse, and, in harmony with this condition, a flora often 

 exceedingly specialized. 



The climate of California is a mild temperate one, due to a 

 A-ariety of causes, and it is modified in various ways by local con- 

 ditions. The southern boundary of the state lies just below lati- 

 tude 32°, and the northern boundary is 10° north of this. With so 

 low a latitude, and with its situation on the western edge of the 

 continent, the state is subject to diying trade winds in summer, 

 and to the moisture laden prevailing westerlies in winter. As a 

 result, the dry season is long, and, especially in the southern 

 portion of the state, semi-desert conditions may prevail. Along 

 the coast, how^ever, due in part to a cold off-shore current, heavy 

 fogs mitigate in a marked manner the severities of the summer 

 drought as well as the summer heat. 



In addition to the periodicity of the rainfall, the amount of rain 

 may vary from year to year to a considerable extent, and, as a rule, 

 where the mean annual rainfall is the least, the irregularity in 

 precipitation is greatest. This feature, the variation in the 

 amount of moisture available to the plants, is of undoubted great 

 importance in shaping the character of the flora of the state. That 



^ Given before the International Phjtogeographic Excursion at Carmel, Cali- 

 fornia, September, 1913. 



22.3 



TUE PLANT WORLD, VOL. 17, KO. S. 1914 



