190 6] SHANTZ—VEGETATION OF THE MESA 23 
following are the velocities in hm. per hour for the different months 
of the year 1904: Jan. 4.6; Feb. 3.3; Mar. 5-7; Apr. 6.09; May 
4.7; June 3.7; July 3.5; Aug. 3.2; Sept. a7) <3 ee oe, 
4.04; Decug-3. 
Temperature-—Extremes in temperature do not occur. The 
summer temperature is seldom above 32°C., and the winter tem- 
perature is seldom —18°C. The maximum temperature recorded 
during the four years 1901-4 was 36°6C., and the minimum for 
the same period --28°3C. The following temperatures are for 
the year rgo4. 
| Jan. | Feb. | Mar. | Apr. | May | June | July | Au. | Sent. | Oct. | Nov. | Dec. 
Maximum.| 17.7 21.6 20.5 | 22.8 | 25.5 | 28.3 | 31.6 | 290.4 | 28.3 | 23.3 | 190.3 18.8 
Minimum .|—18.3 |—18.3 |—14.4 |—9.4 |—1.1 pag 6.1 7.2 5.5/5.5 i$. 5" | —g008 
Mean 42.4 — 2.8 2.2 3-9 7-7") 4251-44507) 28.27) 20-8 1 2903 | 0.4 Sur |e 
| 
The mean temperature is derived from the daily maximum and 
minimum. The daily variation may best be shown by curves from 
the thermograph (jig. 3). 
JULY 29/904 6 
a 
ao 
+—+—+J 
7 
f JAN, 12,1904 | \\ 
aly NM 
en ee ee | 6 |am r | | elm 
Fic. 3.—Daily variation in temperature: 
"4 
Seema stasis asta Sosa 
A comparison of these curves will show clearly how much greater 
is the daily range in winter than in summer. The curve for Jan- 
uary 12, 1901, rises higher than the typical winter curve, but is other- 
wise normal. 
A series of curves showing the variation in temperature between 
the soil, soil surface, plant surface, 10°" above the soil surface, and 
1™ above will serve to show how different are the conditions of 
