VERNAL PHENOMENA IN THE ARID REGION. 
T. DD. A. COCKERELL, 
New Mexico AGRICULTURAL EXPERIMENT STATION. 
Ir has recently! been laid down by Dr. C. H. Merriam that 
“the northward distribution of terrestrial animals and plants 
is governed by the sum of the positive temperatures for the 
entire season of growth and reproduction,” and that “ the south- 
ward distribution is governed by the mean temperature of a 
brief period during the hottest part of the year.” Dr. Merriam 
further explains that, “in computing the sum of the positive or 
effective temperatures, a minimum temperature of 6° C. (43° F.) 
has been assumed as marking the inception of the period of 
physiological activity in plants, and of reproductive activity in 
animals.” Let us now consider the facts as observed at Mesilla 
Park, New Mexico (altitude 3800 feet), and then discuss their 
bearing on Dr. Merriam’s theories. From the meteorological 
data collected by observers at the Mesilla Park Experiment 
Station, I have selected tae PONNE 2 as illustrative : 
iz apris een | MAXIMUM MINIMUM PeR 
E (F.). TEMPERATURE. || TEMPERATURE | NCHES). 
|| 1893. 1896. | 1893. 1896. | 1893. 1896. | 1893 1896. 
January -o o 43-4 | 41-4 73 71 10 9 07 -31 
February... < <i 44.81 ALS 71 75 14 10 || 1.26 -II 
March 9.5. 24 SOOT wri oF 89 21 15 Of | o 
AP fee so eh GS aaa -OF 87 29 23 0 | .II 
May = o 3 2 60 ee 93 | 101 33 31 77 10 
June. a < Si a 77:3 1-765 || 105 104 46 46 00 | 1.01 
The following are the latest dates on which the thermometer 
fell to 30° F. during six years: 
1893- 30° on tis 29. 1896. 29° on April 20 (23° on April 17). 
1394. 30 1 2. 1897. H o~ Ig 
Ios Fe Poy ae S E 
1 Life Zones and C ed Zones of the United States, 1898, ational Geographic 
Magazine, December, 
39 
