Arsenical Poisoning of Fruit Trees. 
55 
The growing apples present a comparatively large amount of sur¬ 
face entirely free from the arsenate of lead and consequently not pro¬ 
tected against the attack of late hatching individuals. These are not 
theoretical considerations but facts as they have been observed in the or¬ 
chard were may be found, in some sections, many apples which the 
worms of the first brood have entered from the side. In such cases 
one spraying would mean a wormy crop. On the other hand the re¬ 
sults obtained with one spraying have been excellent, especially in cases 
where the orchard was not subjected to subsequent infection from adja¬ 
cent, unsprayed, or very poorly sprayed orchards. 
Summary 
While many trees, both apple and pear, have been damaged, even kill¬ 
ed, by the action of arsenic collected about the crown or collar of the tree, 
other causes of death are not excluded. It is shown in Bulletin 155 that 
nitre in the soil may kill apple trees, but the crowns and roots are not at¬ 
tacked by this agent as they are by arsenic. 
The total number of trees affected is large. It is seldom that more 
than a few affected trees occur together, usually they occur singly, scatter¬ 
ed throughout the orchard. 
Trees killed by nitre usually occur in blocks, sometimes only a few 
trees, 12 to 20, but in other instances they occur by the acre. 
The arsenical preparations used for spraying are supposed to be in¬ 
soluble in water, this is not correct. Well washed arsenate of lead will 
yield arsenic acid to pure water, about, 0.3 per cent, of its dry weight. 
The addition of sodic sulfate, sodic chlorid or sodic carbonate, even 
in small quantities, to the water materially increases the amount dissolved. 
This is especially true of the sodic chlorid and sodic carbonate 
In Bulletin 131 , I attached considerable weight to the action of these 
alkali salts which are present in all of the soils of the semi-arid regions 
in a greater measure than in the soils of some other sections. I do not doubt 
but that they have some influence upon the solubility of the arsenical com¬ 
pounds, but as much as 1.38 parts of arsenic acid per million soluble in 
water has been found when the total water-soluble portion amounted to 
only 0.22 per cent, of the air dried soil. Again I have found weighable 
quantities of water soluble arsenic in soils which were free from alkali. 
The alkalis in our soils may increase but they are not the only cause of the 
solubility of the arsenic. 
Three forms of this trouble are recognized, corrosive arsenical poison¬ 
ing, systemic arsenical poisoning and arsenic-lime poisoning. The last 
form is consdered as being produced by the joint action of lime and ar¬ 
senic, because we do not find this trouble present on limestone soils in 
general nor is it characterstic of arsenical poisoning produced by soluble 
arsenic preparations, sodic arsenite for example. 
