246 



The Plant World. 



humidity. In fact, one of the most striking features of this part 

 of California is the differences in rainfall in adjacent localities. 

 The average rainfall on the University Campus may be stated 

 as approximately 16 inches. Within a distance of five miles 

 it increases to between two and three times as great, and at 

 an air-line distance of about twenty miles the average annual 

 rainfall is between 80 and 90 inches. Upon the valley floor 

 snow has fallen, so far as I know, only once in my twelve years' 

 residence here, but on the peaks and sides of the mountains 

 snow falls almost every winter In some winters the snowfall 

 is very light, a mere sprinkling, scarcely visible at a distance; 

 but in seasons of abundant rain, the snow may come far down 

 the mountain sides. In one year the snow remained for several 

 days on the ground as far down as within 1 ,000 feet above sea 

 level. 



In addition to the usual seasons of the temperate zone, 

 the Pacific coast of the United States has two others, with their 

 corresponding effects on vegetation. The rainy season begins 

 in mid-autumn — the first rain usually falls in October — and 

 ends in April. Very rarely does rain fall in June, July, August, 

 and September in the vicinity of this University. It is useless, 

 and frequently injurious, to all forms of agriculture and even to 

 the native plants, when rain does fall out of season. The first 

 rains start the many annuals of the valley floor and of the un- 

 forested slopes, substituting verdure for brownness. Thus we 

 have in autumn what is sometimes called our first spring. Many 

 plants continue to grow throughout the winter, since the frosts 

 do little more than depress the growth-rate. The second spring 

 coincides with the spring of the same latitude elsewhere, only 

 it is richer in bloom than other regions with which I am acquaint- 

 ed. This may be due to the quality and the amount of sunshine. 

 I shall speak of this later. 



The range of temperature in this region is considerable. 

 The mean annual temperature on the Campus is approximately 

 58 degrees Fahrenheit, but the minima and maxima within a 

 period of twenty-five years reached the extremes of 20 degrees 

 and 106 degrees. Between the means of the coldest and the 

 warmest months there may be a difference of 20 degrees, but 

 between the maximum and minimum of a single day there is 



