February, '10] headdex : arsenical poisoning 33 



it into a black friable mass, which may be found of all thicknesses, 

 from thin layers forming scarcely more than a discoloration to masses 

 involving the whole thickness of the bark and the woody tissue under- 

 lying it. We find many trees showing this progressive destruction of 

 the bark and tissues. The same statement holds good for the roots, 

 which are attacked with the crown of the tree. Sun scald, a form of 

 winter injurj^, is an entirely different thing, both in location and 

 appearance; while the bark may be killed in spots, its structure is 

 not destroyed. It is not a blight of any form; a large number of 

 inoculation experiments have been made which have uniformly failed. 



It is not due to the attacks of fungi; these have never been found 

 in these trees in such association with the disease as to even suggest 

 a causal relation. It is not due to drowning or excessive water, for 

 we find cases of badly corroded crowTis in localities where the water 

 plane is many feet below the surface, and a permanent excess of 

 water kills and rots the feeding roots. It is not due to alkali; what- 

 ever we may understand by this term, we have in some districts what 

 is popularly designated ''black alkali." This is not the "black 

 alkali" of California; we have so far as I know absolutely no alkali 

 in Colorado, consisting largely of sodic carbonate. 



There is one occurrence of sodic carbonate in the state, which I 

 described in the American Journal of Science April, 1909. That this 

 so-called black alkali is dangerous and kills trees is true. The active 

 agent in this case is some nitrate, calcic, magnesic or sodic. The 

 crowns of trees killed by this are invariably healthy unless involved 

 by the presence of arsenical poisoning, as may be the case in orchards 

 that have been sprayed. I have seen many trees killed outright in a 

 few 'days by these nitrates. The two cases, i. e., death due to arsenical 

 poisoning and death due to nitre poisoning, are in toto different. 



I have seen one case in which the arsenic had lodged in the crotch 

 of a tree and produced the same results as about the crown. This 

 case was easily distinguished from the effect of snow, etc., lodged in 

 similar places. 



All that has been said so far pertains to the corrosive action of 

 arsenic, but it may be justly asked how may we know that arsenic 

 produces the effects described? Our answer is we have observed the 

 destruction of the bark, the disintegration of the woody tissue and 

 the killing of trees by arsenic. 



So far I have referred to the corrosive action of arsenic when it 



accumulates in the soil about the crown of the tree. There is another 



phase of the question which I believe we find in some orchards much 



more pronouncedly than the one already presented, and this is the 



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