The liFFECT OF Cement Dust on Citkus Trees. 291 



it was impossible that a tree should have a vigorous life and pro- 

 duce an abundant fruitage. 



Incidentally the subject of road dust was taken up, and the 

 horticultural experts agreed that the dust blown from a traveled 

 highway caused the two or three bordering rows of trees to yield 

 less fruit than the same number in the interior of the orchard. 

 One grower had found that it paid him to oil the road passing 

 by his grove in order to prevent this dust. The injury from road 

 dust is, however, much less than that caused by cement dust, 

 as it does not form a scale, and is readily washed off by the winter 

 rains. 



Some testimony on the effect of cement dust on the natural 

 vegetation was not without interest. A slope of the mountain 

 directly facing the old mill, and which receives a very heavy 

 deposit of dust, was occupied by a nearly pure growth of Arte- 

 misia californica. The leaves of this plant, which are narrowly 

 linear, are heavily laden with dust which, however, does not 

 form a scale on them. When cleaned they have a yellowish, 

 sickly color, yet the plants survive, and are not noticeably dimin- 

 ished in number by their copious deluge of dust. This may, 

 then, be counted a dust-resisting species. The next slope, 

 having a different aspect, was formerly covered with Encelia 

 jarinosa, Salvia a plana and S. mellifera, all suffrutescent plants 

 with wider and roughened leaves. Under the dust showers the 

 two latter species have entirely disappeared, and of the former 

 only a few sickly and dying specimens yet remain. 



It appears then that while different plants offer a varying 

 degree of resistance to the deleterious effects of cement dust, all 

 are injured, those whose leaves are deciduous much less than those 

 with persistent leaves. Certainly none are benefitted, as was 

 absurdly claimed by a witness for the defense. The orange and 

 lemon trees whose vigorous life demands an abundant supply of 

 plant food, are peculiarly affected by this interference with that 

 supply. They have become weak and unproductive, and their 

 death is but a question of time. 



San Bernardino, California. 



