80 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
is 2.7° F. greater than that of the air; at 4,000 feet it is 3° F.; at 5,000 
feet, 4.3° F.; at 6,000 feet it is 5.4° F., and at 7,000 feet itis 6.5° F. Inan 
observation made at 4 p.m. August 8, on the western slope of the peak, 
the soil stood at 71.6° F. and the air at 57.6° F., and at 7 a.m. the next 
morning the minimum of 21.2° F. was obtained for the air and 48.2° F. 
for the soil. This increase in the difference between the temperature 
of the soil and the air is due to the increase in intensity of the direct sun’s 
rays and the diminution of the intensity of the diffused radiation by 
reason of the attenuation of the atmosphere at such altitudes. 
No records of the temperature of living plants under such conditions 
are available, but it is evident that the entire subject needs reinvestiga- 
tion by exact methods in which the separate effects of ground radiation 
and direct insolation will be separately accounted for. Such studies 
would be carried out ina system of observations which would embrace 
plantations including identical forms grown at different altitudes. 
7 apgeea TT TTT Rage TF MAREE TRUK (W RES TRAP EAESE TURE 
WE: UT Pert TMT Tat TP TET 
Fan: At ‘bal 
i ia EME aa ata nt PITAL LTT TAY A”, 
‘il ps] [ ny 
LECULAR CLAM PTW PN TET Mi ee TTT 
I VSHAHUTTR AAD ATUOAAEG AUGAAAAUAGS RUT COQ AUREL LUSIAELEPTT 
UTA AN 
SLVOONEUNAUUAL/AN (UULEVUNLGANEDUNNUAUUGAUUTUANANUSVSRUUAUUAUUAYAUUUAUUAANAYSQUNATANLL 
MWA VASA AY 
FSWWSANAALUANUNGSUANULNUANN SUUMALUNUULG SAANURNLNAL 1 \ AANUAAANYSAUBAAUUNNUD SAULLANUD 
TASIMATOLGMEUE: EANAAE ELEC SEEUEE RLGSTEGREA HUGE LuBEAE URGE SLTOEEE ATEBSLEEEES aE 
RETR TTT 
VETERE 
AT 
AC ALLETTTTTTPINGTTTTT NTT 
‘i RT TTA CIAL AHTIN GEE VOLRIA aacoate dni Hl 

Fic. 1.—Meteorological data from San Francisco Mountain, Arizona, August 8 to 
August 19, 1898. The upper curve, traced from the hygroscopic record, shows 
variations in relative humidity. The lower curve shows the corresponding 
air temperature in the shade. (Reprinted from Publication No. 6.) 
Some important results have already come to hand from the investi- 
gations carried on by the Committee on the Relation of Plants to Climate 
of the American Association for the Advancement of Science. 
Dr. MacDougal, to whom the work on soil temperatures was intrusted, 
reported as follows on a series of observations made at a depth of 6 inches 
in the New York Botanical Garden (Monthly Weather Review, August, 
1903): 
