99 



should never liave been planted in such ground, any more than in such 

 as has shallow lying hardpan or clay. (E. W. H.)] 



[" Mottled Leaf." — Closely related in its causes to the "die-back," 

 and sometimes accompanying it, is the " mottled leaf" trouble. It 

 may be properly called "partial chlorosis" of the leaves, and on the ba- 

 sis of that designation it has been attempted to treat it like the cor- 

 responding human ailment, with iron tonics and fertilizers. But in 

 every c ise that I have closely examined, and in most of those reported 

 to me by others who have made such examinations at my suggestion, 

 the cause was not lack of nourishment that could be remedied by such 

 means, but simply an improper con Hi ion of the root system, especially 

 of the deeper roots. When a thriftily growing tree suddenly stops 

 and begins to show mottled leaves, it is clearly not because of lack of 

 nourishment in the soil, but because some of the physical requirements 

 of the tree's well-being have ceased to be satisfied. In such case fer- 

 tilization can afford but temporary relief, if any. 



The commonest cause of mottled leaf is a layer of dry gravel or sand 

 reached by the tap-roots, throwing them out of healthy action. Of 

 course the same effect may be expected from the exhaustion of the 

 usual supply of moisture in the substrata, which has not been made 

 up for by the comparatively scanty irrigation permitted by the dim- 

 inished water-supply during the past three years. The cause of the 

 present great prevalence of mottled or yellow leaf in the citrus or- 

 chards is probably a parallel to the wholesale dying- out of vineyards 

 in the Santa Clara Valley, regarding which a special bulletin (No. 134) 

 was issued by this Station some months ago. 



Quite probably, however, other unfavourable conditions affecting 

 the roots, such as alkali, marl, or a hard-pan layer, may in many 

 cases produce this effect. In any case, the cause should be sought for 

 at the roots before deciding upon possible remedies (E. W. H.)] 



DifjUcidty of Replacing Trees. — It is difficult to install new trees in 

 an orchard when the surrounding trees are large. In fact it is neces- 

 sary to dig very large holes and fill them with rich earth. Such trees 

 should be given extra irrigation alid additional fertilizers, besides 

 what is regularly given to the older trees. This should not be applied 

 merely t > the space around the newly-set trees, but also to the adjoin- 

 ing older trees, as it is needful to furnish enough food and water for 

 all the roots that fill the surrounding soil. 



All orchardists find trouble in filling gaps where trees have died or 

 become diseased, but the difficulties are more marked in the case of 

 citru-? fruits than with the deeper rooting deciduous species. A selec- 

 tion of especially healthy specimens from the nursery will help. Then, 

 as noted, the best of culture and all the fertilizers that can be assimi- 

 lated are needed. Lastly, the judicious root-pruning of large adja- 

 cent trees may assist those newly planted. 



California Orange Standards. 

 Citrus-fruit culture includes much that can find no place in so 

 brief a bulletin, but some of the more pressing and practical problems 

 have been discussed. The interesting topic of wind breaks and hedges 

 for protection against frost and storms has not been taken up, nor has 

 the group of questions relating to the handling and mark-iting of crops. 



