[5]Unless otherwise stated, the climatological statistics given in this paper were taken or compiled from Observations Météorologiques du Riseau Africain, 1907-1908. The evaporation data are based on readings of the Piche evaporimeter. The amount of evaporation given in the text can be reduced to the evaporation from a free-water surface by multiplying by 0.737 (Meteorological Notes, J. I. Craig. Cairo Scientific Journal, vol. vi, May 1912).
[6]At Touggourt, however, no rain was reported during the summer season of 1908.
[7]Kearney and Means, loc. cit.
[8]The Root Habits of Desert Plants. W. A. Cannon. Carnegie Institution of Washington Publication No. 131. 1911. This paper gives a descriptive classification of the main root-types in the deserts of the southwest, in which such a root as found in Acanthyllis is called generalized, in distinction to roots like those of most of the cacti, or Zizyphus, the former having a system wholly superficial and the latter a system wholly deeply placed, as specialized. The specialized root-systems appear to be so fixed in character as to be not easily changed, while the generalized type is flexible. It will be self-evident that the type of root-systems may be of great importance in determining the local distribution of a species.
[9]Compare the root-system of H. scoparium at Biskra, p. [64].
[10]The most striking change in the general character of the vegetation which the traveler notices as he goes from the less arid to the more arid portion of southern Algeria is its decrease in amount. This occurs through dwarfing effects of whatever cause and through a decrease in the number of individuals. Within certain limits the results observed are to be attributed mainly to the first of these, since there is often a surprisingly large number of perennials on any given area. But in other and more intensely arid regions (as portions of the Arabian-Egyptian desert, and indeed a limited area on the hamada between Ghardaia and Ouargla) plants are wholly wanting. Whether such is generally the case on the reg or the hamada farther south in southern Algeria is not known.
[11]Tristram remarks that it “seems that the larger wild animals have been rapidly decreasing in numbers and are in process of speedy extinction. Dr. Shaw, 150 years since, enumerates in his travels . . . five species of ruminants, which from his descriptions must be the bubale, the aoudad or wild sheep, the addax, and the gazelle, as well as the stag. . . . As the population has not increased, but rather retrograded, we can only surmise that the substitution of the flint and steel gun for the matchlock of the Bedouin . . . has been fatal in its results to all larger game.” It may be remarked that the French impose such restrictions on the Arab as regards the character of the guns he may use (only the army and certain officials of the government employing modern arms) that for the region visited Tristram’s description holds fairly well for to-day.
[12]Statistique Générale de l’Algérie, 1908.
[13]Un voyage botanique au Sahara, Bull. Soc. Bot. Belg., 1898.
[14]Massart, loc. cit.