THE WONDERS OF VEGETATION. 69 



God on the sixth day of creation, at the same time with 

 man, to convey an idea of the conditions under which 

 it thrives. The Saharans use a bold but expressive fig- 

 ure : " The king of the oasis," they say, " must plunge 

 his feet in the water and his head in the fire of heaven." 

 Science confirms this assertion in a manner, for it is 

 proved that it requires 9.180 of accumulated heat, 

 spread over eight months, to bring the fruits of the 

 date to maturity. 



" The climate of the Sahara fulfils these condi- 

 tions," adds the great botanist. " The mean tem- 

 perature required is from 68 to 73 according to 

 locality. The heat commences in April and contin- 

 ues to October. During the summer the thermometer 

 reaches 113 and even 125 in the shade. The winter 

 is relatively cold. Dates can endure dry and short 

 cold as low -as 21 above zero and a heat of 122. The 

 radiating sand of the desert cools off more readily than 

 the air, and preserves, at a certain depth, a degree of 

 freshness which invigorates the roots of the trees. 

 Rain is rare in the Sahara ; it falls only in winter and 

 woos the withered plants to a new life. Sometimes 

 it rains in torrents ; but these gusts are of short dura- 

 tion. At Tougourt and Ouargla, whole years pass with- 

 out a drop of rain. Hence the very natural admira- 

 tion of the Arab for this tree with its sweet fruits, 

 which grows in the sand, fed by brackish waters that 

 would be fatal to almost all other plants ; which re- 

 mains flourishing and green when all around is burnt 

 up by the fierce rays of a pitiless sun ; which resists 

 the winds that may bend its pliant plume to the 



