Pl. 32, fig. 73. Detail of square No. 1, on low hills north of Biskra. 74. Vegetation of north slope of the low hills which are north of Biskra. _Ferula vesceritensis_ is the perennial appearing in the figure. Pl. 33, fig. 75. Detail of square No. 2, near area shown in fig. 74. _Ferula_ and _Haloxylon_ are leading species. 76. Root-habit of _Haloxylon scoparium_, from a wash near Biskra. 77. Young shoots and mature roots of _Ferula vesceritensis_. North of Biskra. Pl. 34, fig. 78. Root-habit of _Fagonia_ growing on edge of a wash. Biskra. 79. Large lateral root of _Haloxylon_, with numerous deciduous rootlets, no longer functional. 80. Shoot-habit, taken from above, of _Fagonia_ from the flood-plain of a small oued near Biskra. Pl. 35, fig. 81. Spring annuals, March 17, on north slope of the Djebel Bou Rhezal, Biskra. 82. Root and shoot habit of _Peganum harmala_, Biskra. The main root is especially well developed, although the species has a generalized root-system. Pl. 36, fig. 83. Annuals growing with _Peganum_, near Biskra. 84. General view of the north face of the Djebel Bou Rhezal, Biskra. Apparently barren, plants are rather numerous in the rock crevices and small washes of the mountains. BOTANICAL FEATURES OF THE ALGERIAN SAHARA. * * * * * =INTRODUCTION.= The present paper is designed to give the results of some field-work in southern Algeria in the autumn of 1910 and the spring of 1911. The chief purpose of the tour was to examine the more obvious features of the physiological conditions prevalent in the region in question and, in connection with these observations, to make some detailed studies of the root-habits of the most striking species of the native flora. The route lay through the Atlas Mountains, over the High Plateau, and for some distance into the Sahara itself, returning by a somewhat similar way farther to the east. The country traversed was extremely varied in topography and in plant life, and probably the most southern regions seen may be taken as typical of much of the western Sahara. The distance covered in the more arid portions of the colony was about 1,000 miles. An English-speaking tourist, or any tourist for that matter, is something of a curiosity in southern Algeria. We were said to be the second party of “Englishmen” who had passed over the Ghardaia-Ouargla country in twenty-five years.