GHARDAIA. 49 



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 ever- 

 greens, 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 meas- 

 urements. 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.) 



The evergreen shrub Capparis spinosa has the largest leaves of any plant 

 native to the Ghardaia region, and probably of southern Algeria. Its leaves 

 are bilateral and nearly round and are placed upright on the branches; a 

 series of 29 leaves from one branch 33 cm. long varied from 2 to 3.2 cm. 

 in length and slightly less in width, the average being, length 2.9 cm., 

 breadth 2.2 cm. 



Euphorbia guyoniana has a deciduous leaf -habit. Its leaves are rather 

 small but numerous. A shoot 22 cm. long bore 40 leaves varying in length 

 from 1.5 to 2.1 cm. and in breadth from 1.2 to 2.0 mm., with the average 

 length and average breadth 1.7 cm. and 1.6 mm. respectively. 



It is worth noting that the surface of the leaves, as shown by inspection, 

 is, possibly, most often smooth, as, for example, in Capparis, Henophyton, 

 and Haloxylon. Dense hairiness is an exception among the species seen, 

 Lithospermum callosum being the only plant striking in this regard. 



GROWTH AND FLOWERING HABITS IN THE GHARDAIA REGION. 



Upon arriving at Ghardaia in November, it was surprising to find several 

 species of perennials, under strictly desert conditions, putting on new 

 growth, forming fresh leaves, or coming into flower. Especially was this 



