The Botanical Aspects of Stanford University. 247 



commonly as great a difference. "Reliable frost data are not 

 available," * but during the winter of 1899-1900 the common 

 garden nasturtium (Tropaeolum) vegetated all winter in my 

 garden, quite unprotected. In every other year, however, this 

 plant has been killed by frost On the other hand, a few hun- 

 dred feet above the floor of the valley, what is commonly called 

 a "frostless belt" runs along the foothills. Within this, edible 

 oranges are grown on a commercial, though small, scale. 



Another condition greatly affecting vegetation also deserves 

 mention, namely, the invisible water- vapor in the air, and the 

 fog. Humidity tables, if taken by themselves, would mislead 

 a visiting botanist. In fact, I think their value to any student 

 of the vegetation of this region is slight because of the great dif- 

 ferences in the humidity of the air over the open country and 

 in the wooded canyons. Among the wooded canyons themselves 

 there are considerable differences according to their direction, 

 whether they are or are not the channels in which the fog-streams 

 flow through the mountains from the ocean into the valley. In 

 these fog-channels the air is damp and cool even in mid-summer, 

 while elsewhere it is dry and may be hot. The rainfall is greater 

 in these fog-channels than on the valley floor; but naturally I 

 can not substantiate this statement by figures, for the country- 

 is still too sparsely populated to yield the data. The loss of 

 water from the soil by evaporation is least where the rainfall is 

 heaviest and vice versa. This results from the topography 

 previously described. 



The main source of water for plants, cultivated and wild, 

 on the floor of the valley is the gravel beds underlying the sur- 

 face alluvium.** But this source is supplemented, to an extent 

 wholly unknown, or even capable of estimate at the present time, 

 by* the fogs. In the vicinity of this University fogs may come 

 through the mountain passes from the ocean, or they may be 

 so-called land or Bay fogs. The latter exercise less influence 

 on the vegetation than the former, owing to their duiation and 

 the times~of their occurrence. In summer they are brief and 

 come about sunrise, if at all, in the winter they may last much 



•McAdie, A. G. Climatology of California. U. S. Dep't of Affile.: Weather Bureau. 

 Bull. L. Washington, 1903. 



** Branner. J C . Newborn. J. F. Arnold. R Otologic Atlas of the United States 

 Santa Cruz Folio, California. U. S. Geologic Survey. Washington. 1909. 



