326 BOTANICAL GAZETTE [APRIL 
along with those representing the growth of the palms, coincides 
in general with them, with one exception. Both years the rate of 
growth was maintained late into the fall considerably in excess of 
the amount of heat available. This may have been due to the con- 
tinuance of the great activity which the plant experienced during 
the late summer and early fall months; that is, it was in better 
condition to utilize the available heat at this time than at a corre- 
sponding period in the spring. 
The curves for the rate of growth show.it to be the most active, 
not at the period of highest maximum, but rather at that of the 
highest minimum temperatures, which means warm nights. This 
falls in July, August, and sometimes September; and it is at this 
time that weakly palms recover their vitality. By far the greater 
part of the total yearly growth falls in the last half-year. The 
spring growth is much less luxuriant than the fall growth. The ~ 
warm nights of July and August are due to the somewhat increased 
humidity, which prevents the usual rapid radiation after sun- 
down. Humidity in itself is undoubtedly an important factor, 
but probably has less to do with the rate of growth of date palms 
than with other plants. 
The chief relations of temperature to the rate of growth of date 
palms according to these measurements are: first, the period of 
maximum growth coincides with that of highest minimum rather 
than with that of highest maximum temperature, and this falls 
during the summer period of highest relative humidity; second, the 
rate of growth throughout the entire year is, in most cases, in Pf 
portion to the heat-time units over 50° F. 
The rate of maturation of the fruit is probably influenced by the 
same factors as the rate of growth of the foliage. The effect of 
high minimum temperature in promoting the maturing and ve ai 
ing of the Deglet Noor date has recently been called to the writers 
attention by M. Briguez, the civil governor of Gafsa in Southern 
unis. The oasis of Gafsa, which lies not over 75 miles northeast 
of the Djerid region, where the finest Deglet Noor dates are DEC: 
duced, produces only second quality fruit. The difference in alti- 
tude between the two oases is about goo feet, Gafsa being 1126 
feet and Tozeur in the Djerid 197 feet. The two are separated by 
