SOIL AND CLIMATE. 43 



Assuming that the data from both investigators are correct, it 

 seems that the explanation of the case would most likely be found 

 from a comparison either of the heights of the temperatures at 

 the different stages of the fruiting season, or of the amounts of 

 rainfall at the ripening time. Unfortunately Swingle does not 

 give the monthly rainfalls and maximum and minimum tempera- 

 tures at Ayata for the particular years which he refers to, and 

 I have not yet got these to hand, so I am not able to say whether 

 they throw any light on the point. 



He notes, however, that in 1889 when the dates are said to 

 have ripened well at Ayata, the rainfall for the whole year was 

 only 2*52 inches ; in 1890, when they ripened very imperfectly, 

 it was 9 '32 inches, and that again in 1891, when they ripened 

 imperfectly, it was 4*16 inches. It appears to me possible, there- 

 fore, that in 1890 and 1891 enough rain may have fallen, when 

 the fruits were ripening, to have spoiled them somewhat. This 

 suspicion is strengthened by the fact that the finest dates can 

 be grown at Nefta, where there is practically no rain under 3,277F. 

 units, and that several first class varieties are grown at 

 Kebili which is practically rainless until October or November, 

 under 3,183F. units. Our data indicate that 2,738F. units is 

 too little heat to ripen first class dates properly, as at Gafsa, which 

 is practically rainless, the finest dates do not appear to do so. 

 From the Alexandria figures, it appears that lower qualities of 

 dates can be ripened where there are about 2,000 units of heat 

 properly distributed between 1st May and 31st October.* No 

 dates appear to ripen under 1,373 units distributed throughout 

 the season as at Algiers (For monthly mean temperatures at 

 Nefta, Kebili, Gafsa, Biskra, Orleansville, Algiers, etc., seepage 31, 

 Table VII, and for a comparison of the data to hand concerning 

 humidity and rainfall, see Tables XIII, XIV, XV, XVI and XVII, 

 pages 46, 47, 48, 49, 50 and 51). The relative qualities of date 

 fruits grown at the places where the sums oi the heat units lie 

 between those of Alexandria and Nefta appear to correspond 

 roughly with these sums. 



* Some dates in Alexandria ripen in early September. 



