Note 8 — LAGHOUAT.

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.