34 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



a spreading shrub, frequently attaining a height of 3 to 4 meters, with 

 branches well armed with stout spines. The leaves are small, simple, and 

 leathery. (Compare fig. 14.) The spines are so efficient as a means of pro- 

 tection that the shrub shows no signs of being eaten by animals, although, 

 as quoted above, Massart remarks that after his camels had gone five days 

 without food they ate the jujube branches in spite of the spines. 



The unarmed betoum and the armed jujube have a very interesting 

 relationship, which is as follows : When the seeds of the betoum germinate 

 the seedling is eagerly eaten by animals if it chances, as is usually the case, 

 that the germination occurs on the open daya floor; but if the seeds are 

 carried to a Zizyphus and germinate in its midst, the young plants may 

 attain to a considerable height before being seen by animals, and, being 

 protected by the encircling jujube, will continue growing until they are 

 too large to be easily killed through grazing. It usually happens that once 

 the betoum plant appears above the top of the protecting shrub the camels 

 attempt to reach the attractive shoots and the jujube is trodden under 

 foot. The jujube is thus ultimately destroyed and a mound around the 

 base of the young betoum is all of it that remains. If the jujube is relatively 

 small and the developing betoum is discovered while still small, it will be 

 much eaten, and probably killed; but if it reaches a considerable height 

 before the discovery is made, only the lower branches will be devoured and 

 the specimen will survive. Massart was unable to find any young betoums, 

 but when my visit to Tilrempt was made, November, 19 10, there were 

 several, although so well hidden as to cause much trouble in finding them. 

 A view of one of these is shown in fig. 13. 



The betoum is eaten by the gazelle as well as by domestic animals, which 

 are abundant enough in this region, and this fact is probabfy of great 

 influence in restricting its distribution. Fairly numerous on the desert at 

 present, according to Tristram the gazelle was very abundant in earlier 

 times; he speaks of their tracks marking the plain like sheep-walks. 



From what we have already seen regarding the ill effect of grazing, it 

 will appear that the relation between the betoum and the jujube is a very 

 vital one to the former; and it probably is not too much to say that the 

 distribution of the betoum in the daya region is entirely dependent on that 

 of the jujube, since there is no other armed shrub in the region to afford 

 the protection essential to its survival; with relatively favorable moisture 

 conditions, considerable depth of soil, and a protecting jujube, the betoum 

 will flourish and reproduce now quite as well as in former years. 



THE CHEBKA. 



No dayas were seen after leaving Tilrempt, and the aspect of the country 

 changed markedly and suddenly as the drainage became better defined. 

 The hills were more abrupt and in systems, and the valleys became broad 

 and continuous. At first the valleys were wide and shallow, the hills being 



