30 University of California Puhlications in Botany [Vol. 9 



The data given in the temperature table (table 7) shows that little 

 difference exists in the first month of the year between the mean 

 temperatures of Summit and Fordyce, the slightly higher mean tem- 

 peratures of Summit being due to the fact that, though the monthly 

 maxima are never as high at this season as at Fordyce, the monthly 

 minima are always higher than at the lower station. That this rela- 

 tively mild late winter at Fordyce is not due to its comparatively low 

 altitude is shown by comparison with Bridgeport which, at the same 

 altitude, is the coldest of the five stations. Indeed, this contrast be- 

 tween localities of equal altitude but on opposite sides of the range 

 is observed within much shorter distances than that separating For- 

 dyce and Bridgeport. In the quadrennium here considered, Tahoe, 

 though 270 feet lower than Fordyce, has a lower mean temperature 

 through January, February, and March, and practically the same 

 mean temperature in April ; not until May is there much difference 

 between the monthly means of Fordyce and Tahoe in favor of the 

 latter place. 



Stud}' of the diagram indicates that, as the j^ear advances, Fordyce 

 becomes relatively colder until in late summer and early fall it is 

 the coldest station of the series. On the other hand, Bridgeport, the 

 coldest station through all the winter months (November to March) 

 becomes the warmest station immediately after the end of the winter 

 precipitation season. The vegetation at Bridgeport passes from a 

 mean monthly temperature in March, 7.3° below freezing, to a mean 

 temperature 7.8° above the zero point, in April. The diagram shows 

 that at no other point is the transition to the vernal season so abrupt. 

 Plant phj'siologists are agreed that vegetation may endure consider- 

 able absolute range of temperature with less injury if the change be 

 graduated over a period of some length than an abrupt change of less 

 absolute amount. The gradual change in the position of Fordyce in 

 spring and summer has been referred to; in the fall this locality again 

 shows a relative rise. The temperature element in the local climate 

 of Fordyce has a yearlj^ range the most moderate of any of the 

 stations; it is the only locality where minima less than freezing are 

 not recorded while its summer maxima are no higher than those of 

 Tahoe. The ratio of the mean of the coldest month to the mean of 

 the warmest month at Fordyce is less than at any other station — 

 100 :184.5. 



A study of the temperature conditions at Tahoe shows, as indicated 

 in the diagram, that this station is also for one month in the year the 



