4 BULLETIN 271, U. S. DEPARTMENT OF AGRICULTURE. 



when taken in connection with a fruit as exacting in temperature 

 requirements as the date it becomes of very great importance. 



Another important factor in the environment of the date tree is 

 the relative humidity of the air, which along the Mediterranean coast, 

 where there is an extensive culture, is very high throughout the year. 

 At Alexandria, with a record of 23 years, the mean monthly range of 

 relative humidity is from 64 to 72 per cent, with an annual mean of 

 68, some years running to 71 per cent. At Gizeh the mean relative 

 humidity of a 10-year record is 69 per cent, with single monthly 

 means as low as 50 and as high as 84 per cent. At Heluan the desert 

 influences begin to be felt, and the mean relative humidity is reduced 

 to 54 per cent, and at Siut (Assiut) it is 53 per cent. Aswan gives a 

 record of 39 per cent humidity as a mean for 11 years, while the Oasis 

 of Dakhleh, on a record of 7 years, shows real desert dryness, with a 

 mean humidity of only 36 per cent, and Wadi Haifa, on a 20-year 

 record, has the low mean of 34 per cent. 



No weather records are available for the Sukkot region, formerly so 

 important, but now superseded in the volume of date production by 

 Dongola Province. Merowe, the capital of Dongola, fortunately has 

 very complete records for recent years and shows the greatest dryness 

 of any date region yet studied, its mean relative humidity for the year 

 being only 24 per cent. For May, the driest month, the record is only 

 12 per cent on a 5-year mean; 30 per cent in August and 31 per cent 

 in January, the most humid months. 



Passing the fourth and fifth cataracts with considerable date culture 

 in Berber Province, at the next weather station, Atbara Junction, 

 influenced by the nearness of the rainy hill region on the east and 

 southeast, the mean humidity rises to 38 per cent, reaching 50 per cent 

 in August, with occasional records for April and May as low as 16 per 

 cent. At Khartum, beyond which few date trees are found, the mean 

 humidity for the year drops to 33 per cent. 



For convenience in studying the character of the dates produced as 

 related to their environment, the region under consideration may be 

 divided as follows : 



(1) The maritime subtropical: Comprising Lower Egypt, or the 

 Nile delta, including lower Gizeh. 



(2) The desert subtropical: Comprising Upper Egypt to Aswan, 

 with the Libyan oases. 



(3) The desert tropical: Comprising Upper Egypt beyond Aswan 

 and the Nile Valley in the Sudan at Khartum. 



Hard and fast lines are difficult to draw, and if there were a greater 

 number of observation stations it is probable that points on the mar- 

 gin of the delta toward the desert, like Salihieh and Korain on the 

 eastern border of the delta and Manshia to the west of Gizeh, would 

 show temperature and humidity conditions which would place them 



