The Botanical Aspects of Stanford University 240 



valley is less bright than that of this part of California. The 

 differences in the composition of the air as regards moisture, 

 dust, and smoke entail qualitative and quantitative differences 

 in the absorption of light by the air of different regions. Ten 

 hours of sunshine will not necessarily give New York, Ohio, 

 Nebraska, and California the same amounts or the same qual- 

 ities of light. There will be differences in the proportions of the 

 so-called luminous, thermal, and actinic rays as well as in the 

 total amounts of sunlight. These differences I can not state; I 

 can only suggest them for consideration. Valuable as are the 

 tables published by the Weather Bureau, the physiological 

 botanist wishes that he could know more about the sunlight of 

 any given region than is indicated by records of "clear, partly 

 cloudy, and cloudy " days and the "percentage of possible sun- 

 shine." So slight a difference in the brightness of daylight that 

 neither the trained eye nor the available instruments can deter- 

 mine it will be responded to on a spring morning here by the flow- 

 ers of Eschscholzia, Calandrinia, etc.; they will remain closed or 

 they will open accordingly. Taking into account the work of 

 Delpino, Klebs, Voechting, and their followers regarding flower- 

 ing and the other forms and stages of reproduction, one must 

 admit the probable importance of the influence of sunlight on 

 the reproductive function in plants. * The prodigality of bloom 

 described by John Muir, the yields of giains and fruits, the quan- 

 tities of seeds of forest trees, the productivity of the smaller 

 plants of this region, must be attributed in part to illumination, 

 superior in quality and in quantity, as well as to the more readily 

 determined factors of temperature, soil-fertility, water supply, 

 etc. 



I think I have thus laid the foundation in this discussion 

 of the topographical and climatic conditions, for a description 

 of the vegetation of the environs of Stanford University. Let 

 me summarize, however, what I have so far said, before I pro- 

 ceed to more. We have here, within a day's walk of the Univer- 

 sity buildings, a range in elevation from sea-level to 3,000 feet; 

 a range in average annual rainfall from 15 to 80 or 90 inches; 

 a range in temperature from 20 degrees to 106 degrees Fahren- 

 heit, with a mean near 58; a range in humidity from 20% or 30% 



*See Peirce. G. J. Text-book of Plant Physiology, p. 274 + 



