40 THE DATE PALM. 



From a comparison of the above tables, it appears that the 

 mean temperatures for the whole of the world's date-fruiting 

 season (1st May to 31st October) at all the Punjab stations are 

 higher than that at Nefta ; that the monthly mean temperatures 

 in the same season are higher at Montgomery, Multan, Khushab, 

 and Sirsa than those at Nefta ; that those at Lahore and Ludhiana 

 are all higher than at Nefta, except in August when they are only 

 0'8F. and r8F. lower, respectively ; that those at Delhi, Sialkote, 

 and Amballa are higher, except in July and August, when they 

 are lower by less than 3'5F. ; that at Rawalpindi they are only 

 short of those at Nefta by 21 F. in July, 4'2F. in August, 2'5F. 

 in September, 0'9F. in October, and are far better than those 

 at Cairo where many date trees are successfully farmed. 



So far as mean temperatures in the date-fruiting season are 

 concerned, therefore, it seems that the very best dates known 

 could be grown at Montgomery, Multan, Khushab, and Sirsa ; 

 probably also at Lahore and Ludhiana, while Delhi, Sialkote, 

 and Amballa fall little short of the standard required for first 

 class dates ; and even at Rawalpindi the temperatures are quite 

 suitable for date farming. 



19. It has been stated that, with certain reservations, 

 . certain amounts of heat are required to produce 



Comparison 01 



Heat-Units at Pun- flowers and to mature the fruits of particular 



jab stations with 



those at stations in crops. People holding this view have made 



Algeria, Tunis, 



Egypt, and Meso- comparison of the sums of daily temperatures 



potamia. . . .. 



with a view to throwing light on whether a plant 

 w r ould mature in a certain district, and if so, on what date it 

 would be likely to mature. The daily mean temperatures are 

 usually added for this purpose. Ihe value of comparisons of this 

 sort has been severely criticised. It has been contended that 

 these comparisons can only be made between regions of somewhat 

 similar climates, and some people deny the value of that, pointing 

 out that the amount and nature of the plant's food supply, the 

 supply of water, the amount of light, etc., are equally vital 

 factors in the development of the plant. Where the sunshine is 

 little interrupted by cloud, etc., and the plants are in moderately 



