EXAMPLES OF DROUGHT EESISTANCE. " 25 



This purpose is accomplished most effectively and in the most 

 characteristic way of all by that typical desert tree, the majestic 

 palm ( Washingtonia filifera) , whose dying lower leaves suspended by 

 their long petioles form a dense thatch, completely insulating the 

 tall, columnar, branchless trunk against both the direct and reflected 

 heat of the sun and the drying winds. Wliere some vandal hand 

 does not apply a torch, this splendid protection is retained for many 

 years, perhaps for life. 



It is probable that in the case of the olive, as well as of many native 

 desert plants, this low, spreading canopy of top serves another purpose. 

 Of the total precipitation for the year in these regions a considerable 

 proportion is in the form of small showers, so that the monthly record 

 will often be indicated by such fractions of an inch as 0.12, 0.09, 0.32, 

 0.06, trace, etc., these usually representing a single precipitation. 

 Such an amount falling upon the parched soil in the open is so soon 

 evaporated as to afford little aid to the thirsty plant. Arrested by 

 the leaves or fine branches and carried to the ground at the base of 

 the stem, it is so shaded and conserved as to be allowed to sink into 

 the surface soil, where a system of short, finely branched supei-ficial 

 roots is ready to appropriate it. In Plate IV, figure 2, such rootlets of 

 the olive tree are shown in natural size. 



Inspection of the whole 26 acres of the plantation shows that sev- 

 eral varieties were set, just what they were being difficult to decide 

 with accuracy, no plat or planting list so far having been discovered. 

 The block in which the most trees are alive and in the best condition, 

 though not making the largest growth, has the dense, compact habit 

 and broad top most completely developed, and here any exposure of 

 trunk or main branches to the sun is hard to find. These trees are 

 noticeable for the complete absence of any sun scald on the bark. 



The northern seventeen rows of this block are ranker in growth and 

 more coarsely branched, and while the leaves are larger the whole 

 canopy is much thinner. Of this variety, probably Manzanillo, a 

 quarter of the trees are dead and others have suffered severe sun scald. 

 In other cases a portion of the top has died back, to be followed by a 

 vigorous sprouting from below. Of a block of four rows adjacent to 

 this, not 10 per cent of the trees are alive, but these appear to be of a 

 variety little adapted to these conditions. 



The cottonwoods already referred to, bounding the 20-acre block 

 on the west and north sides, are all dead, but so also are the olive 

 trees next to them. Of the Manzanillo olives, the two rows on the 

 north and next to the cottonwoods are two-thirds dead, while the 

 third row is in bad condition. 01" the trees on the west ends of the 

 rows next to the cottonwoods in the larger block not so large a propor- 

 192 



