SOIL AND CLIMATE. 45 



the Punjab. The dry atmosphere, which allows an excessive 

 heating during the day, allows an equally great fall of tempera- 

 ture at night by radiation of heat into a cloudless sky; therefore 

 the diurnal range of temperature in dry parts of the season is 

 much greater than it is in damp weather (see page 33, para. 18). 

 Damp or rainy weather is directly injurious to date palms 

 in preventing the fertilisation of the flowers in spring and 

 in causing decay or dropping of the fruit when it is developing 

 and ripening in summer. Tables XIII, XIV, XV, XVI and XVII, 

 on pages 46 51 show the mean relative humidities and normal 

 rainfalls at stations in Tunis, Algeria, Egypt, Mesopotamia, 

 Persian Gulf, and the Punjab. 



21. The date flowering season in the Tunis oases appears 



to be from about the middle of March to the 

 middle of April (see Kearney, page 53, Bulletin 

 No. 92, United States of America, Department 

 of Agriculture) ; that for the Algerian oases appears to begin in 

 April and extend to the end of May (see Swingle, page 27, Bulletin 

 No. 53, United States of America, Department of Agriculture) ; 

 April-May cover the chief flowering seasons in Lower Egypt, and 

 March-April that of Upper Egypt, Dakhla oasis, Baghdad, and 

 the Punjab. For our purpose, we may take the spring months, 

 March, April, and May, as the world's flowering season. 



22. From the figures to hand an average humidity of 63 



in the spring months apparently does not 

 H fl U owiring 8 sea S om interfere with date culture, as Tozer, where large 



quantities of some of the finest dates known are 

 cultivated, has that degree of humidity. A normal mean humidity 

 of 73-74, even at that season, does not appear to be a serious 

 objection, as at Port Said under that humidity, hand pollination 

 is successfully carried on. The point for intending date growers 

 to note when comparing climates as regards humidity and rainfall 

 in the flowering season is whether hand pollination ensures 

 fertilisation in a sufficiently high percentage of cases. Con- 

 trasted with the places just referred to, the mean relative humi- 

 dities at all the Punjab stations in that season seem satisfactory. 



