SAIDY DATE OF EGYPT. 31 
Comparing first the Dakhla Oasis with the Mecca garden in Cali- 
fornia, both points having an excess of heat above the requirements of 
the Saidy, date, we may note that Dakhla has higher annual means 
(both maximum and minimum) by 3.5° or 4° F. than Mecca, but the 
Dakhla curves are broader ones, showing much higher maxima for 
March, April, and May. nearly the same as Tempe and Mecca from 
June to September, but with Mecca about 3° F. hotter in August. The 
Mecca minima are above those of Dakhla for both July and August. 
Xow. from the deductions relative to the temperature of Baharia 
made in a previous paragraph we must presume that the tempera- 
tures at Mecca more closely approximate those of Baharia than those 
•of Dakhla. What Table i does not show is the occurrence of actual 
frost temperatures in Dakhla. but, quoting from the same authority, 
absolute minima of 0° C. were recorded in both January and Feb- 
ruary between 1905 and 1911. though the writer has been assured that 
nothing more than light frosts are ever experienced there. 
At Mecca, on the other hand, there is an average of 20 frosty nights 
in the year, and the lowest annual minima of the record for 10 years 
range from 13° to 26° F. Fortunately, these extreme minimum tem- 
peratures endure for only a short period, usually not exceeding 30 
minutes, as shown by the thermograph trace, and the frost never 
penetrates the growing center, though at 13° to 17° F. most of the 
outer leaves were killed. 
Comparing the Dakhla records with those of Heluan, the mean 
maxima at Heluan are found to be from G° to 11° F. lower 
throughout the year, the greatest difference being for the month of 
May. The mean minima for the year are nearly the same for Dakhla 
and Heluan, but the curies cross about March 15 and September 15 — 
that is, Heluan has warmer nights in autumn, winter, and spring, 
but the nights are cooler than at Dakhla from the middle of March 
to the middle of September. Heluan is practically frostless, though 
Gizeh shows minima in January as low as —2.5° C, or 27.5° F. 
The harvest in the Xile Valley is prolonged to about two weeks 
later than in Dakhla. Frost would not interfere with the Nile Valley 
harvest before the new year, but the relative humidity at Heluan, 
always higher than at Dakhla, advances to 58 per cent in September 
and October and 62 per cent in November, while at Gizeh the hu- 
midity reaches 72 per cent in September and 75 per cent in October. 
It is evident that this upper Gizeh district has little heat to spare for 
the ripening of a choice packing date, and it is probable that it is 
practical cultural experience that has confined the field of culture of 
this date to the territory from Gizeh southward. 
Our next inquiry should be, why this date, whether derived from 
the Libyan Oasis or from Gizeh, has failed to mature fruit at the 
Tempe garden. The annual mean maximum for Tempe is 85.7° F., 
only 1° below that of Mecca, where both the Libyan and Gizeh Saidy 
strains have ripened perfectly, some years early in September. The 
Tempe maximum carve is above the Heluan curve throughout the 
year, except for falling slightly below in Xovember and December. 
It i^ far above it. practically with Dakhla, during June, July, August, 
and September. 
It is to the Tempe minimum curve that we must look for an expla- 
nation of the failure to mature fruit of this variety. This curve falls 
