DATES OF EGYPT AND THE SUDAN. 15 
Algerian Deglet Noor trees from offshoots brought to Merowe were 
shown to the writer by Gov. Jackson in first fruit, and in the latter 
part of September the fruits were ripe and as hard as the dry dates 
of the country. This same tendency to become dry or ‘‘mummified” 
is observed in the Deglet Noor in the Coachella Valley in California 
in exceptionally dry, hot seasons, especially if a minimum amount of 
water is given them. 
The preponderance of dry dates in the Nubia and Sudan portions 
of the Nile Valley may, then, be attributed to two general causes, 
namely, the general tendency of the climate to the production of dry 
varieties and the selection of such dry varieties as are of greatest 
commercial value. Such selection is on account of the readiness 
with which they are cured and the convenience with which they are 
stored and transported, their indestructible character permitting their 
being packed in stout bags and carried by camel caravans subject to 
the hardest conditions, yet always ready as an article of food without 
preparation. 3 | 
Referring to the temperature diagrams in figure 1 and the plotted 
curves in figure 2, 1t will be seen that at Merowe and Khartum the 
lowest monthly means, December and January, are considerably 
- above the line of 64.4° F., assumed to be the zero point of activity 
of the date tree in flowering and fruiting functions. In spite, how- 
ever, of the high December and January means, the date trees of 
Dongola flower and are pollinated at about the usual time of dates 
farther north. According to Davie, ‘‘pollination takes place in Ieb- 
ruary and March,” practically the same months when it is practiced 
in Dakhleh and Khargeh, where the means of December and January 
are considerably below 64.4° F. That is, a continuous mean tem- 
perature for those months of several degrees above the assumed zero 
point does not prevent these trees from having a resting period and 
postponing the flowering period to about the season when it occurs 
in considerably cooler localities. Davie records that the fruit at 
Merowe ripens about seven months after pollination, or September 
and October, but at the time of the writer’s visit to Merowe, on 
September 20, nearly all the dates had been gathered, the Barakawi 
harvest had ended practically a week previously, and much of the 
fruit was being marketed. These facts point strongly to the necessity 
of a study of date-tree activities from another standpoint than that 
of a mean temperature of 64.4° F. as the zero point.! 
1Dr. A. E. Vinson, of the Arizona Agricultural Experiment Station (in Botanical Gazette, vol. 37, p. 
324-327), describes the rate of leaf growth of two trees each of the Deglet Noor and Rhars varieties at the 
cooperative date garden, Tempe, Ariz., through the growing seasons of 1906 and 1907 and calls attention to 
the agreement of the rate of growth with the mean minimum rather than with the mean maximum tem- 
peratures of the period studied. His diagrams are, however, too much involved with the waning growth 
of the successive leaves as they approach maturity to make his conclusions convineing. In fact, his growth 
curves show a more intimate coordination with the surface-soil temperature than with any other factor. 
