GHARDAIA. 47 



On the southern side of the oued, where the soil is cemented into a sort 

 of hardpan, E. guyoniana grows in greater abundance, frequently in groups 

 but also singly. Other observations confirm those above reported, namely, 

 that the species reproduces largely vegetatively, new plants springing from 

 old roots, which at Ghardaia are essentially water- and food-storage organs. 

 Only two other species were seen to have water-storage capacity, namely, 

 Citrullus colocynthis, to be described directly, and Phelypaa violacea, which 

 was seen at Biskra and will be described later. 



In the habitat of Peganum, and a few meters distant, was found a speci- 

 men of Henophyton deserti, which had been little injured by flocks. The 

 shoot of the plant was about 30 cm. high, and, in spite of the long dry 

 season, was in full leaf. It possessed a long tap-root, of which 75 cm. was 

 recovered. No laterals were given off along the portion of the root seen. 

 Other specimens of the same species were also examined, and in every 

 instance a similar type of root was found. 



Somewhat nearer the side of the valley, but growing where there was 

 considerable depth of sand, were several specimens of Tamarix, the roots 

 of one of which were partly exposed. The plant studied was over 3 meters 

 high and had not been injured by animals. Its root was of the tap-root 

 type, since the main root went unbranched directly downward. 



There occur in the valley a few specimens of Citrullus colocynthis de- 

 scribed by Schimper, in "Plant Geography," as follows: 



A cucurbitaceous plant resembling our cultivated pumpkin, and its long, juicy, rel- 

 atively thick-foliaged and large-leaved shoots remain green throughout the summer, 

 producing fruits as large as a child's head. It presents, therefore, the appearance of 

 being protected in an unusual manner against the loss of water. As a matter of fact, 

 however, severed shoots dry up in a few minutes. The extraordinary length of the 

 roots of colocynth alone renders its existence possible in the desert. 



While the description of Schimper is a good one, it conveys the idea of 

 much greater luxuriance of growth than was observed for the species at 

 Ghardaia. As a matter of fact, the leaves of this plant are small and much 

 dissected, and the fruit is the size of an orange. How deeply the roots 

 penetrate the ground, or their length, was not learned, but a very striking 

 characteristic of the root is its fleshiness, which is shown by fig. 37. anc * tne 

 ability of the species to successfully withstand drought may lie in the fact 

 that it is thus provided with a very well-developed and very well-protected 

 water-storage organ, as much as in having a great length of root. Citrullus 

 occurs typically where there is considerable depth of earth, especially close 

 to oueds, although it is rarely to be found on the plain and only where the 

 soil is deepest. In the latter habitat the possibility of a permanent con- 

 nection with a perennial water-supply is without question excluded. The 

 species is rather to be considered one of the forms, rare to the Sahara, 

 which possess a water-balance, and which has the power of storing sufficient 

 water during the widely separated rainy seasons to last it during the period 



