412 
Journal of Agricultural Research 
Vol XXXI, No 5 
temperature for this period were quite evenly about two hours apart, 
the shape of the trace showing only slightly less time in the cooling 
operation than in the rise to the higher temperature at which the 
machine started again. The line of 47°, as the mean, divides this 
trace as equally as it can be done. 
Since even in a cold chamber so shallow as this the difference in 
the temperature between the top and bottom air is considerable, 
these palms were laid down so as to bring them as nearly as possible 
on a level with the recording thermograph. 
Though palms Nos. 2 and 3 were in turn placed in the cool chamber 
or used as controls in the greenhouse air, the history of palm No. 1 
is so typical that its description will serve for all: 
Palm No. 1, with a leaf in active growth, marked for record, was 
placed in air conditions in the greenhouse at about 70° day tempera¬ 
ture and made 9 mm. growth in two days. It was transferred to the 
cool chamber at 4.40 p. m. on August 29, where, at a mean tempera¬ 
ture of 53°, growth dropped at once to 0.5 mm. daily. 
Except a short perioa when the machine stopped and the chamber 
temperature ran up to 62°, the growth averaged 0.45 mm. daily for 
14J^ days. Palm No. 3, placed in the cool chamber September 14 
under the same temperature range, made 17.4 mm. of growth in 15 
days. This continuous activity under prolonged exposure to these 
temperatures so near the zero point is an important fact which could 
not have been disclosed under field conditions. 
Palm No. 1 was next transferred to the greenhouse, where day 
temperatures were 70° to 77°, and made 1 mm. daily gain for two 
days, then the rate rose to 3 mm. daily. For 10 days under green¬ 
house conditions the mean daily gain was 2.4 mm. Again placed in the 
cool chamber September 24, with a temperature averaging 53.5°, this 
palm made a daily average gain of 1 mm. for the next six days. From 
noon of September 30 to noon of October 2 the temperature of the 
cool chamber was lowered to a range of from 49° to 54°, and from 
noon of the 2d until noon of the 5th it ranged from 46° to 52°. 
During the first two days no gain in growth was registered, but a 
gain of 0.6 mm. was made during the following three days at the 
lower temperature. With the maxima above 50° only six and one- 
fourth hours, or 8.7 per cent of this time, this close approach to the 
zero mark is very significant, as a similar reduction in growth was 
recorded for the two other plants which were in the cold chamber 
at this period. 
Because of the wide range in temperature allowed by the thermo¬ 
stat, it is not certain at this critical period whether this slight growth 
should be credited to the brief periods when the temperature was 
above 50° or whether some part of it may have been made at tem¬ 
peratures slightly lower. During the next two days (from noon of 
October 5 until 9 a. m. October 7), with the temperature ranging 
from 44.5° to 49.5°, growth on all three plants entirely ceased. Here 
again the lapse of time during which the temperature was above 49° 
or below 45° was so small as to be negligible, but the time with the 
temperature above 48° was six and one-half hours, or 14 per cent 
of the whole period. This was time enough to have permitted a trace 
of growth had this been within the growth zone of temperature. By 
these tests, then, the positive exclusion of growth lies below 49°, 
with room for doubt whether any growth was made below 50°. 
