LATE FROSTS AND DRAINAGE OF COLD AIR. 61 



THE DATE PALM FLOWERS LATE IN SPRING AND ESCAPES INJURY 



BY LATE FROSTS. 



A very great advantage of the date palm is that it flowers late in 

 spring, after all danger of frost is over," whereas many other fmit 

 trees, among them the peach, the apricot, and especially the almond, 

 bloom very early and are exposed to much risk of having the flowers 

 or } T oung fruits killed by late frosts. 



The records available from the Sahara are very poorly calculated to 

 show how much cold the date palm can stand, for the whole northern 

 and western Sahara is characterized by very warm winters. Tempera- 

 tures of 5 to 7 C (21.4 to 23 F.)are recorded from date oases in the 

 Sahara, but the date palm is able to endure lower temperatures than 

 these without serious harm resulting. The northern limit and the 

 limit in altitude in northwestern Africa at which dates can be grown 

 are set more by the deficient summer heat failing to ripen the fruit 

 than by the cold in winter. 6 



DRAINAGE OF COLD AIR AND INVERSION OF TEMPERATURE IN 

 RELATION TO DATE CULTURE. 



A peculiarity of climate which is of considerable importance in 

 relation to date culture is the inversion of temperature which occurs 

 in many places in Arizona and California, and more markedly in arid 

 regions where the date palm succeeds best. For example, in many 

 parts of Arizona the winters are mild enough to permit date palms to 

 be grown at an altitude of nearly 5,000 feet, and even as high as 6,942 

 feet at Supai. It is noticeable, however, that points very much lower 

 frequently show temperatures sufficiently cold to injure severely or to 

 kill date palms. For instance, at San Carlos, at an altitude of 2,456 



The pistache nut has the same advantage and can be grown with profit in place 

 of the almond in many localities where the latter is likely to lose its fruit because of 

 late frosts. 



&It is probable that the date palm is hardier than has been supposed, and that by 

 selecting hardy sorts and wrapping them well when young, date culture can be ex- 

 tended to many of the desert regions in the Southwest hitherto supposed to be too 

 cold in winter for this plant. The experiments at the date garden at Tulare have 

 shown that there is a great difference in the resistance of the various sorts to cold, the 

 Seewah at an age of 9 years being, for instance, 12 feet high, with a spread of leaves 

 of 15 feet, while the Sultaneh, equally old but which had been much hurt by the cold 

 winters was only 4 feet high, with a spread of leaves of 7 feet. The experience of the 

 winters of 1901-1902 at Tempe, Ariz., has shown that recently transplanted offshoots 

 are hardier than has been supposed. It now becomes a matter of much importance 

 to procure hardy sorts of date palms (probably best to be secured in the oases of Per- 

 sia and Baluchistan) for planting in the deserts in the south western United States which 

 have hot summers but cold winters. Fort Mclntosh, altitude 460 feet, in south- 

 western Texas, and Fort Thomas, altitude 1,600 feet, in the valley of the Virgin River 

 in southern Nevada, both have a summer climate hotter than that of Phoenix, in the 

 Salt River Valley, Arizona, but at- the same time colder winters. Late sorts of dates 

 of good quality could be matured at these places provided they could pass the winters 

 unharmed (see pp. 126 and 134). 



