Up to this point the plants whose roots have been described were found growing where the soil was favorable to a fairly normal development, but the soil of the valley is not all of this character, and where hardpan is present the substratum is often extremely hard and, one would think from inspection, impermeable to water as well as impenetrable to roots. In such habitats the number of individuals and also of species is very naturally limited. About 2 kilometers west of Ghardaia is an area where the hardpan reaches nearly or quite to the surface. Here _Peganum harmala_ is to be found, since its generalized type of root-system is capable of not a little variation, adjusting the species to a variety of soil conditions not otherwise possible. Associated with _Peganum_ was a single specimen, of dwarfed and badly eaten form, growing out of the hardpan itself. The position of the plant was so unusual that its root-system was in part excavated. The form, an undetermined chenepod, was found to have the exceptional form of root, thus proving the rule just suggested, for it had a well-marked tap-root. A gnarled main root was found to take a zigzag course through 27 cm. of hardpan to the softer stratum beneath. The root did not follow a crack, but struck boldly downward through soil so hard that it was removed by the use of a sharp iron instrument and only with great difficulty. LEAF-HABITS IN THE GHARDAIA REGION. Observations of the leaf characters of the desert perennials, as shown in November, offer some points of interest, especially since there had been no rain for a year previous to the visit. As would be expected, the leaf-habit is various, ranging from scale-like or none to fair size. Several species appear to be evergreen, including _Artemisia herba-alba_, _Capparis spinosa_, _Echium humilis_, _Fagonia bruguieri_, _Gymnocarpon_ sp., _Haloxylon articulatum_, _Helianthemum sessiliflorum_, _Henophyton deserti_, _Herniaria fruticosa_, and _Salsola_. Certain plants probably, as _Henophyton_, are facultative evergreens, retaining the leaves if the season is moist and dropping them if it is excessively dry; several of this genus were seen without leaves, but with green stems. (See, also, figs. 39, 40, and 41.) Some idea of the variation in size of the leaves of a single species, as well as the average size of the leaves, will be had from the results of a few measurements. The leaves of _Henophyton deserti_ range in length from 2 to 3.1 cm., and in breadth from 0.2 to 0.5 cm. The average length of 12 leaves from a single branch 7 inches in length was found to be 2.82 cm.; the average breadth was 0.35 cm. On another branch, 23 cm. long, were 35 mature leaves which averaged almost exactly the size of those just given. Since these leaves are rather numerous and of good size, it will appear at once that the species has a relatively large leaf-surface, even if the area can not be stated more definitely. (Fig. 30.)