SURPLUSES AND DEFICIENCIES 197 



possibility of the absorption through the stomata and cuticle of the fruit 

 of quantities sufficient to cause local poisoning in the apple, giving rise 

 to the disorder known as bitter pit. 



Manganese. — The relation of an excess of manganese to iron deficit 

 and the method of curing the diseased condition have been discussed. 

 In excess, this element produces interesting symptoms, illustrated by 

 pineapples grown on manganese soils. 



The root system is reduced by the death of a large percentage of the fine 

 branched rootlets some months after their formation. The roots that remain 

 alive have a superabundance of root hairs, almost every epidermal cell elongating 

 into one, and also a blunt growing tip, about half as large as a lead pencil, 

 frequently swollen into an enlarged fleshy end. The formation of these 

 enlargements seems to mark the end of growth and death soon follows. The 

 leaf has an irregular surface due to shrinkage from loss of water, producing 

 prominences which become dark brown. The cells have brown walls and 

 in some cases the protoplasm eventually disintegrates. The green cells thus 

 lose their color, become plasmolized and in some cases the nuclei turn brown. 

 Here also the protoplasm loses its granular structure and disintegrates. As a 

 result of the lack of chlorophyll, the leaves contain limited amounts of starch, 

 but at the base of the leaves, in the stalks and roots, starch is abundant, having 

 been stored there before the decomposition of the chlorophyll. Frequently no 

 fruit develops, but that which does is reddish pink, without a trace of green, 

 undersized and excessively acid.>°^ 



Apparently manganese poisoning is rare in deciduous fruits. In 

 very dilute amounts manganese has a stimulating effect. ^^ 



Other Elements. — Compounds of many other elements such as lead, 

 mercury, zinc, boron^^ and silver are toxic in certain concentrations, but 

 toxic effects from them are rare. However, these materials are known 

 occasionally to be absorbed in considerable quantities — zinc for example 

 up to 13 per cent, of the ash, mercury and copper up to 1 per cent.®^ 

 Ewert^^ has shown that extremely minute quantities of these, in con- 

 centrations varying from 1 in 1,000,000 to 1 in 1,000,000,000, may 

 cause local browning in the tissues of the fruit of the apple and induce the 

 condition known as bitter pit. 



Mention may be made here of certain toxic gases such as hydrogen 

 sulfide, sulfur dioxide, hydrogen cyanide and chlorine. Sulfur dioxide 

 injury is of considerable practical importance because the damage done 

 to vegetation by smelter fumes is due largely to this compound. 



The bulk of the evidence on the toxicity of inorganic mineral soil 

 constituents that has been discussed, suggests that the effects are largely 

 local in the plant. Amounts small enough to be stimulating are unques- 

 tionably absorbed by the roots, or in the case of spraying, by the leaves, 

 but amounts large enough to poison the plant seem to induce injury 

 chiefly by affecting the absorbing organs. Hence cessation of growth 



