414 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
temperature. Growth may continue at a reduced rate when the 
minimum air temperatures are several degrees below the freezing 
point, provided the maximum temperatures of the days are well 
above a minimum of 50° F. 
Observations at the United States date garden at Indio, Calif., 
show that with minimum temperatures above the freezing point but 
with the maxima of the days reduced to from 46° to 50° F., growth 
of four date palms, after a characteristic lag, has been found to have 
entirely ceased. A specific zero point or minimum of temperature 
for growth of between 46° and 50° F., but varying slightly with the 
individuals, has been deduced from these records. 
Young date palms in pots placed for 14 days in a controlled tem¬ 
perature bench in a greenhouse at a temperature varying but slightly 
from 53° F. made daily growth of from 0.5 to 1 mm., ana slight gains 
were recorded at from 49° to 50°. Below 49° all growth ceased. 
The plants experimented with in the greenhouse cool chamber when 
placed in greenhouse benches at day temperatures of about 68° F. 
resumed their normal rate of growth in darkness without appreciable 
delay. The laboratory tests thus confirm the previous field observa¬ 
tions. 
The conclusion is reached that the zero point, or minimum tempera¬ 
ture permitting, growth of the date palm, lies at from 48° to 50° F. 
for the actual region of cell division and growth, and that this knowl¬ 
edge is fundamental to the study of the reactions of these trees to 
other temperature conditions. 
