THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 57 



last at S** 15". Those toward the end are therefore comparatively 

 a trifle too low. In the computation the highest value obtained 

 (at station 5) is taken as unity and the others are reduced to decimals 

 in proportion. In the observations of sun intensity the instrument 

 was pointed directly toward the sun. In the spotty shade of the 

 chaparral it was moved about continually during the exposure, so 

 that an average figure was obtained. 



The great differences in the direct sunlight intensities are appar- 

 ently due to differences in amount of reflected and diffused light, 

 the chaparral stations, with much bare light-colored soil naturally 

 being the highest, and the forest, with dark soil and much vegetation, 

 the lowest. The shade differences are less than might be expected. 



Tempehatuke. 



In the matter of atmospheric temperature there is an unfortunate 

 shortage of data. Isolated observations of so variable a factor, 

 even though numerous, are of little value. The thermograph is the 

 only satisfactory apparatus for habitat study, and no thermographs 

 were available for the work. Some knowledge of comparative 

 temperature values during the dry season may be gained from two 

 series of observations (table 10), obtained during trips over the 

 trail connecting the stations. The first was made during the middle 

 of the daj^, the second between 3 and 4 p. m. The readings were 

 made from the dry bulb of the cog psychrometer in the process of 

 measuring relative humidity. 



The outstanding feature is the uniformity of temperature. No 

 differences of moment occur between any of the stations, nor be- 

 tween sun and shade. The latter would, of course, not be true if 

 the sun had been allowed to shine on a stationary bulb. The 

 probable effect in such a case is roughly indicated by the high sun 

 temperatures recorded in the surface lines of the soil temperature 

 graph (fig. 13). As the air readings stand, the shade temperature 

 in the Adenostoma stations is in nearly every case higher than the 

 sun temperatures, while in the other stations the reverse is true. 

 The reason in the former case is not clear. 



